draft-ietf-pim-dr-improvement-04.txt   draft-ietf-pim-dr-improvement-05.txt 
PIM WG Zheng. Zhang PIM WG Zheng. Zhang
Internet-Draft Fangwei. Hu Internet-Draft Fangwei. Hu
Intended status: Standards Track BenChong. Xu Intended status: Standards Track Benchong. Xu
Expires: June 13, 2018 ZTE Corporation Expires: December 30, 2018 ZTE Corporation
Mankamana. Prasad Mishra Mankamana. Mishra
Cisco Systems Cisco Systems
December 10, 2017 June 28, 2018
PIM DR Improvement PIM DR Improvement
draft-ietf-pim-dr-improvement-04.txt draft-ietf-pim-dr-improvement-05.txt
Abstract Abstract
PIM is widely deployed multicast protocol. PIM protocol is defined PIM is widely deployed multicast protocol. PIM protocol is defined
in [RFC4601] and [RFC7761]. As deployment for PIM protocol growing in [RFC7761]. As deployment for PIM protocol is growing day by day,
day by day, user expect least traffic loss and fast convergence in user expects lower traffic loss and faster convergence in case of any
case of any network failure. This document provides extension to network failure. This document provides extension to the existing
existing defined protocol which would improve stability of PIM protocol which would improve stability of PIM protocol with respect
protocol with respect to traffic loss and convergence time when the to traffic loss and convergence time when the PIM DR is down.
PIM DR is down.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 13, 2018. This Internet-Draft will expire on December 30, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PIM hello message format . . . . . . . . . . . . . . . . . . 3 3. PIM hello message format . . . . . . . . . . . . . . . . . . 3
3.1. DR Address Option format . . . . . . . . . . . . . . . . 4 3.1. DR Address Option format . . . . . . . . . . . . . . . . 4
3.2. BDR Address Option format . . . . . . . . . . . . . . . . 4 3.2. BDR Address Option format . . . . . . . . . . . . . . . . 4
4. The Protocol Treatment . . . . . . . . . . . . . . . . . . . 4 4. The Protocol Treatment . . . . . . . . . . . . . . . . . . . 4
4.1. Election Algorithm . . . . . . . . . . . . . . . . . . . 5 4.1. Deployment Choice . . . . . . . . . . . . . . . . . . . . 5
4.2. Sending Hello Messages . . . . . . . . . . . . . . . . . 6 4.2. Election Algorithm . . . . . . . . . . . . . . . . . . . 6
4.3. Receiving Hello Messages . . . . . . . . . . . . . . . . 7 4.3. Sending Hello Messages . . . . . . . . . . . . . . . . . 7
4.4. The treatment . . . . . . . . . . . . . . . . . . . . . . 8 4.4. Receiving Hello Messages . . . . . . . . . . . . . . . . 8
4.5. Sender side . . . . . . . . . . . . . . . . . . . . . . . 9 4.5. The treatment . . . . . . . . . . . . . . . . . . . . . . 9
4.6. Sender side . . . . . . . . . . . . . . . . . . . . . . . 9
5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 9 5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Deployment suggestion . . . . . . . . . . . . . . . . . . . . 9 6. Deployment suggestion . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . 10 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. Normative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
Multicast technology is used widely. Many modern technology use PIM Multicast technology is used widely. Many modern technologies, such
technology, such as IPTV, Net-Meeting, and so on. There are many as IPTV, Net-Meeting, use PIM-SM to facilitate multicast service.
events that will influence the quality of multicast services. The There are many events that will influence the quality of multicast
change of unicast routes will cause the lost of multicast packets. services. Like the change of unicast routes, the change of the PIM-
The change of DR cause the lost of multicast packets too. SM DR may cause the loss of multicast packets too.
When a DR on a share-media LAN is down, other routers will elect a After a DR on a shared-media LAN went down, other routers will elect
new DR until the expiration of Hello-Holdtime. The default value of a new DR after the expiration of Hello-Holdtime. The default value
Hello-Holdtime is 105 seconds. Although the value of Hello-Holdtime of Hello-Holdtime is 105 seconds. Although the minimum Hello
can be changed by manual, when the DR is down, there are still many interval can be adjust to 1 second and the Hello-Holdtime is 3.5
multicast packets will be lost. The quality of IPTV and Net-Meeting times Hello interval. Thus, the detection of DR Down event cannot be
will be influenced. guaranteed in less than 3.5 seconds. And it is still too long for
modern multicast services. Still, may multicast packets will be
lost. The quality of IPTV and Net-Meeting will be influenced.
\ / \ /
\ / \ /
------- ------- ------- -------
| A | | B | | A | | B |
------- ------- ------- -------
| DR | | DR |
| | | |
------- ------- ------- -------
| SW |-----------------------------| SW | | SW |-----------------------------| SW |
------- ------- ------- -------
| | | |
Figure 1: An example of multicast network Figure 1: An example of multicast network
For example, there were two routers on one Ethernet. RouterA was For example, there are two routers on one Ethernet. RouterA is
elected to DR. When RouterA is down, the multicast packets are elected to DR. When RouterA is down, the multicast packets are
discarded until the RouterB is elected to DR and RouterB imports the discarded until the RouterB is elected to DR and RouterB imports the
multicast flows successfully. multicast flows successfully.
We suppose that there is only a RouterA in the Ethernet at first in We suppose that there is only a RouterA in the Ethernet at first in
Figure 1. RouterA is the DR which is responsible for forwarding Figure 1. RouterA is the DR which is responsible for forwarding
multicast flows. When RouterB connects the Ethernet, RouterB will be multicast flows. When RouterB connects to the Ethernet segment,
elected to DR because a higher priority. So RouterA will stop RouterB will be elected as DR because of its higher priority. So
forwarding multicast packets. The multicast flows will not recover RouterA will stop forwarding multicast packets. The multicast flows
until RouterB joins the multicast group after it is elected to DR. will not recover until RouterB pulls the multicast flows after it is
elected to DR.
So if we want to increase the stability of DR, carrying DR/ BDR role
information in PIM hello packet is a feasible way to show the DR/ BDR
roles explicitly. It avoids the confusion caused by new comers which
has a higher priority.
2. Terminology 2. Terminology
Backup Designated Router (BDR): A shared-media LAN like Ethernet may Backup Designated Router (BDR): Like DR, A BDR which acts on behalf
have multiple PIM-SM routers connected to it. Except for DR, a of directly connected hosts in a shared-media LAN. But BDR MUST not
router which will act on behalf of directly connected hosts with forward the flows when DR works normally. When DR is down, the BDR
respect to the PIM-SM protocol. But BDR will not forward the flows. will forward multicast flows immediately. A single BDR MUST be
When DR is down, the BDR will forward multicast flows immediately. A elected per interface like the DR.
single BDR is elected per interface like the DR.
Designed Router Other (DROther): A router which is neither DR nor
BDR.
3. PIM hello message format 3. PIM hello message format
In [RFC4601] and [RFC7761], the PIM hello message format was defined. In [RFC7761], the PIM hello message format is defined. In this
In this document, we define two new option values which are including document, we define two new option values which are including Type,
Type, Length, and Value. Length, and Value.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| Hello message format | | Hello message format |
| | | |
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| OptionType + OptionLength | | OptionType + OptionLength |
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| OptionValue | | OptionValue |
skipping to change at page 4, line 44 skipping to change at page 4, line 44
o OptionLength: If the network is support IPv4, the OptionLength is o OptionLength: If the network is support IPv4, the OptionLength is
4 octets. If the network is support IPv6, the OptionLength is 16 4 octets. If the network is support IPv6, the OptionLength is 16
octets. octets.
o OptionValue: The OptionValue is IP address of BDR. If the network o OptionValue: The OptionValue is IP address of BDR. If the network
is support IPv4, the value is IPv4 address of BDR. If the network is support IPv4, the value is IPv4 address of BDR. If the network
is support IPv6, the value is IPv6 address of BDR. is support IPv6, the value is IPv6 address of BDR.
4. The Protocol Treatment 4. The Protocol Treatment
Carrying DR/ BDR role information in PIM hello packet is a feasible
way to keep the stability of DR. It avoid the confusion caused by
new comers which has a higher priority. So there are some changes in
PIM hello procedure and interface state machine.
A new router starts to send hello messages with the values of DR and A new router starts to send hello messages with the values of DR and
BDR are all set to 0 after its interface is enabled in PIM on a BDR are all set to 0 after its interface is enabled in PIM on a
share-media LAN. When the router receives hello messages from other shared-media LAN. When the router receives hello messages from other
routers on the same share-media LAN, the router will check if the routers on the same shared-media LAN, the router will check if the
value of DR is filled. If the value of DR is filled with IP address value of DR is filled. If the value of DR is filled with IP address
of router which is sending hello messages, the router will store the of router which is sending hello messages, the router will store the
IP address as the DR address of this interface. IP address as the DR address of this interface.
Then the new router compare the priority and IP address itself to the Then the new router compares the priority and IP address itself to
stored IP address of DR and BDR according to the algorithm of the stored information of DR and BDR according to the algorithm of
[RFC4601] and [RFC7761]. If the new router notices that it is better [RFC7761]. If the new router notices that it is better to be DR than
to be DR than the existed DR or BDR. The router will make itself the the current DR or BDR. The router will make itself the BDR, and send
BDR, and send new hello messages with its IP address as BDR and new hello messages with its IP address as BDR and current DR. If the
existed DR. If the router notices that the existed DR has the router notices that the current DR has the highest priority in the
highest priority in the share-media LAN, but the existed BDR is set shared-media LAN, but the current BDR is set to 0x00000000 if IPv4
to 0x0 in the received hello messages, or the existed BDR is not addresses are in use or 0:0:0:0:0:0:0:0/128 if IPv6 addresses are in
better than the new router, the new router will elect itself to BDR. use in the received hello messages (To be simplify, we use 0x0 in
If the router notices that it is not better to be DR than existed DR abbreviation in following parts of the draft), or the current BDR is
and BDR, the router will respect the existed DR and BDR. not better than the new router, the new router will elect itself to
BDR. If the router notices that it is not better to be DR than
current DR and BDR, the router will follow the current DR and BDR.
When the new router becomes the new BDR, the router will join the When the new router becomes the new BDR, the router will join the
existed multicast groups, import multicast flows from upstream current multicast groups, import multicast flows from upstream
routers. But the BDR MUST not forward the multicast flows to avoid routers. But the BDR MUST not forward the multicast flows to avoid
the duplicate multicast packets in the share-media LAN. The new the duplicate multicast packets in the shared-media LAN. The new
router will monitor the DR. The method that BDR monitors the DR may router will monitor the DR. The method that BDR monitors the DR may
be BFD technology or other ways that can be used to detect link/node be BFD technology or other ways that can be used to detect link/node
failure quickly. When the DR becomes unavailable because of the down failure quickly. When the DR becomes unavailable because of the down
or other reasons, the BDR will forward multicast flows immediately. or other reasons, the BDR will forward multicast flows immediately.
4.1. Deployment Choice
DR / BDR election SHOULD be handled in two ways. Selection of which DR / BDR election SHOULD be handled in two ways. Selection of which
procedure to use would be totally dependent on deployment scenario. procedure to use would be totally dependent on deployment scenario.
1. When new router is added in existing steady state of network, if 1. The algorithm defined in [RFC7761] should be used if it is ok to
the new router notices that it is better to be DR than the existing adopt with new DR as and when they are available, and the loss caused
DR. It does elect itself as DR as procedure defined in RFC 7761. by DR changing is acceptable.
This method must be used when user is ok to have transition in
network. This option should be used if deployment requirement is to
adopt with new DR as and when they are available, and intermediate
network transition is acceptable.
2. If the new router notices that it is better to be DR than the 2. If the deployment requirement is to have minium packets loss when
existed DR or BDR, the router will make itself the BDR, and send new DR changing the mechanism defined in this draft should be used. That
hello message with its IP address as BDR and existed DR. Uses of is, if the new router notices that it is better to be DR than the
this option would have less transition in network. This option current DR or BDR, the router will make itself the BDR, and send new
should be used when deployment requirement is to have minimum hello message with its IP address as BDR and current DR.
transition in network unless there is some failure.
4.1. Election Algorithm According to section 4.9.2 defined in [RFC7761], the device receives
unknown options Hello packet will ignore it. So the new extension
defined in this draft will not influence the stability of neighbor.
But if the router which has the ability defined in this draft
receives non-DR/BDR capable Hello messages defined in [RFC7761], the
router MAY stop sending DR/BDR capable Hello messages in the LAN and
go back to use the advertisement and election algorithm defined in
[RFC7761].
4.2. Election Algorithm
The DR and BDR election is according the rules defined below, the The DR and BDR election is according the rules defined below, the
algorithm is similar to the DR election definition in [RFC2328]. algorithm is similar to the DR election definition in [RFC2328].
(1) Note the current values for the network's Designated Router and (1) Note the current values for the network's Designated Router and
Backup Designated Router. This is used later for comparison Backup Designated Router. This is used later for comparison
purposes. purposes.
(2) Calculate the new Backup Designated Router for the network as (2) Calculate the new Backup Designated Router for the network as
follows. Those routers that have not declared themselves to be follows. The router that has not declared itself to be Designated
Designated Router are eligible to become Backup Designated Router. Router is eligible to become Backup Designated Router. The one which
The one which have the highest priority will be chosen to be Backup have the highest priority will be chosen to be Backup Designed
Designed Router. In case of a tie, the one having the highest Router Router. In case of a tie, the one having the highest Router ID is
ID is chosen. chosen.
(3) Calculate the new Designated Router for the network as follows. (3) Calculate the new Designated Router for the network as follows.
If one or more of the routers have declared themselves Designated If one or more of the routers have declared themselves Designated
Router (i.e., they are currently listing themselves as Designated Router (i.e., they are currently listing themselves as Designated
Router in their Hello Packets) the one having highest Router Priority Router in their Hello Packets) the one having highest Router Priority
is declared to be Designated Router. In case of a tie, the one is declared to be Designated Router. In case of a tie, the one
having the highest Router ID is chosen. If no routers have declared having the highest Router ID is chosen. If no routers have declared
themselves Designated Router, assign the Designated Router to be the themselves Designated Router, assign the Designated Router to be the
same as the newly elected Backup Designated Router. same as the newly elected Backup Designated Router.
skipping to change at page 6, line 47 skipping to change at page 7, line 10
Router and Backup Designated Router, although that router will never Router and Backup Designated Router, although that router will never
be the calculating router (Router X) itself. The elected Designated be the calculating router (Router X) itself. The elected Designated
Router may not be the router having the highest Router Priority. If Router may not be the router having the highest Router Priority. If
Router X is not itself eligible to become Designated Router, it is Router X is not itself eligible to become Designated Router, it is
possible that neither a Backup Designated Router nor a Designated possible that neither a Backup Designated Router nor a Designated
Router will be selected in the above procedure. Note also that if Router will be selected in the above procedure. Note also that if
Router X is the only attached router that is eligible to become Router X is the only attached router that is eligible to become
Designated Router, it will select itself as Designated Router and Designated Router, it will select itself as Designated Router and
there will be no Backup Designated Router for the network. there will be no Backup Designated Router for the network.
4.2. Sending Hello Messages 4.3. Sending Hello Messages
According to Section 4.3.1 in [RFC4601] and [RFC7761], when a new According to Section 4.3.1 in [RFC7761], when a new router's
router's interface is enabled in PIM protocol, the router send hello interface is enabled in PIM protocol, the router sends Hello messages
messages with the values of DR and BDR are filled with 0x0. Then the with the values of DR and BDR are filled with 0x0. Then the
interface is in waiting state and start the hold-timer which is like interface is in Waiting state and start the hold-timer which is equal
the neighbor hold-timer. When the hold-timer is expired, the to the Neighbor Liveness Timer. When the timer is expired, the
interface will elect the DR and BDR according to the DR election interface will elect the DR and BDR according to the DR election
rules. rules.
When a new router sets itself BDR after receive hello messages from When a new router sets itself BDR after receive hello messages from
other routers, the router send hello messages with the value of DR is other routers, the router send hello messages with the value of DR is
set to the IP address of existed DR and the value of BDR is set to set to the IP address of current DR and the value of BDR is set to
the IP address of the router itself. the IP address of the router itself.
When a existed BDR sets itself non DR and non BDR after receive hello A current BDR MUST set itself DROther after it receives Hello
messages from other routers, the router will send hello messages with messages from other routers, the router will send hello messages with
the value of DR is set to existed DR and the value of BDR is set to the value of DR is set to current DR and the value of BDR is set to
new BDR. new BDR.
DR newcomer DR newcomer
\ / \ /
----- ----- ----- ----- ----- -----
| A | | B | | C | | A | | B | | C |
----- ----- ----- ----- ----- -----
| | | | | |
| | | | | |
------------------------------------------- LAN ------------------------------------------- LAN
Figure 3 Figure 3
For example, there is a stable LAN that include RouterA and RouterB. For example, there is a stable LAN that includes RouterA and RouterB.
RouterA is the DR which has the best priority. RouterC is a RouterA is the DR which has the best priority. RouterC is a
newcomer. RouterC sends hello packet with the DR and BDR is all set newcomer. RouterC sends hello packet with the DR and BDR is all set
to zero. to zero.
If RouterC cannot send hello packet with the DR/BDR capability, If RouterC cannot send hello packet with the DR/BDR capability,
Router C may send the hello packet according the rule defined Router C MAY send the hello packet according the rule defined in
in[RFC4601] and [RFC7761]. [RFC7761].
If deployment requirement is to adopt with new DR as and when they If deployment requirement is to adopt with new DR as and when they
are available, a new router with highest priority or best IP address are available, a new router with highest priority or best IP address
sends hello packet with DR and BDR all set to zero at first. It sends hello packet with DR and BDR all set to zero at first. It
sends hello packet with itself set to DR after it finish join all the sends hello packet with itself set to DR after it finish join all the
existing multicast groups. Then existed DR compares with the new existing multicast groups. Then current DR compares with the new
router, the new router will be final DR. router, the new router will be final DR.
4.3. Receiving Hello Messages 4.4. Receiving Hello Messages
When the values of DR and BDR which are carried by hello messages are When the values of DR and BDR which are carried by hello messages are
received is all set to 0x0, the router MUST elect the DR using received is all set to 0x0, the router MUST elect the DR using
procedure defined in [RFC4601] and [RFC7761] after the hold-timer procedure defined in DR election algorithm after the hold-timer
expires. And elect a new BDR which is the best choice except DR. expires. And elect a new BDR which is the best choice except DR.
The election cases can be executed as following:
In case the value of DR which is carried by received hello messages In case the value of DR which is carried by received hello messages
is not 0x0, and the value of BDR is set to 0x0, when the hold-timer is not 0x0, and the value of BDR is set to 0x0, when the hold-timer
expires there is no hello packet from other router is received, the expires there is no hello packet from other router is received, the
router will elect itself to BDR. router will elect itself to BDR.
In case either of the values of DR and BDR that are carried by In case either of the values of DR and BDR that are carried by
received hello messages are larger than 0x0. The router will mark received hello messages are larger than 0x0. The router will mark
the existed DR, and compare itself and the BDR in message. When the the current DR, and compare itself and the BDR in message. When the
router notice that it is better to be DR than existed BDR. The router notice that it is better to be DR than current BDR. The
router will elect itself to the BDR. router will elect itself to the BDR.
When a router receives a new hello message with the values of DR and When a router receives a new hello message with the values of DR and
BDR are set to 0x0. The router will compare the new router with BDR are set to 0x0. The router will compare the new router with
existed information. If the router noticed that the new router is current information. If the router noticed that the new router is
better to be DR than itself, or the new router is better to be BDR better to be DR than itself, or the new router is better to be BDR
than the existed BDR, the router will set the BDR to the new router. than the current BDR, the router will set the BDR to the new router.
When existed DR receives hello packet with DR set larger than zero, When current DR receives hello packet with DR set larger than zero,
algorithm defined in section 4.1 can be used to select the final DR. algorithm defined in section 4.1 can be used to select the final DR.
As illustrated in Figure 3, after RouterC sends hello packet, RouterC As illustrated in Figure 3, after RouterC sends hello packet, RouterC
will not elect the DR until hold-timer expired. During the period, will not elect the DR until hold-timer expired. During the period,
RouterC should receive the hello packets from RouterA and RouterB. RouterC should receive the hello packets from RouterA and RouterB.
RouterC accepts the result that RouterA is the DR. In case RouterC RouterC accepts the result that RouterA is the DR. In case RouterC
has the lowest priority than RouterA and RouterB, RouterC will also has the lowest priority than RouterA and RouterB, RouterC will also
accept that Router B is the BDR. In case RouterC has the accept that Router B is the BDR. In case RouterC has the
intermediate priority among the three routers, RouterC will treat intermediate priority among the three routers, RouterC will treat
itself as new BDR after the hold-timer expired. In case RouterC has itself as new BDR after the hold-timer expired. In case RouterC has
the highest priority among the three routers, RouterC will treat the highest priority among the three routers, RouterC will treat
RouterA which is the existed DR as DR, and RouterC will treat itself RouterA which is the current DR as DR, and RouterC will treat itself
as new BDR. If the network administrator thinks that RouterC should as new BDR. If the network administrator thinks that RouterC should
be new DR, the DR changing should be triggered manually. be new DR, the DR changing should be triggered manually.
Exception: During the hold-timer period, RouterC receives only the Exception: During the hold-timer period, RouterC receives only the
hello packet from RouterA. When the hold-timer expired, RouterC hello packet from RouterA. When the hold-timer expired, RouterC
treats RouterA as DR. and RouterC treats itself as BDR. In case treats RouterA as DR. and RouterC treats itself as BDR. In case
RouterC only receives the hello packet from RouterB during the hold- RouterC only receives the hello packet from RouterB during the hold-
timer period, RouterC will compare the priority between RouterB and timer period, RouterC will compare the priority between RouterB and
itself to elect the new DR. In these situations, some interfaces or itself to elect the new DR. In these situations, some interfaces or
links go wrong in the LAN. links go wrong in the LAN.
4.4. The treatment 4.5. The treatment
When all the routers on a shared-media LAN are start to work on the When all the routers on a shared-media LAN are start to work on the
same time, the election result of DR is same as [RFC4601] and same time, the election result of DR is same as [RFC7761]. And all
[RFC7761]. And all the routers will elect a BDR which is suboptimum the routers will elect a BDR which is next best to DR. The routers
to DR. The routers in the network will store the DR and BDR. The in the network will store the DR and BDR. The hello messages sent by
hello messages sent by all the routers are same with the value of DR all the routers are same with the value of DR and BDR are all set.
and BDR are all set.
When a new router start to work on a shared-media LAN and receive When a new router start to work on a shared-media LAN and receive
hello messages from other routers that the value of DR is set. The hello messages from other routers that the value of DR is set. The
new router will not change the existed DR even if it is superior to new router will not change the current DR even if it is superior to
the existed DR. If the new router is superior to existed BDR, the the current DR. If the new router is superior to current BDR, the
new router will replace the existed BDR. new router will replace the current BDR.
When the routers receive hello message from a new router, the routers When the routers receive hello message from a new router, the routers
will compare the new router and all the other routers on the LAN. If will compare the new router and all the other routers on the LAN. If
the new router is superior to existed BDR, the new router will be new the new router is superior to current BDR, the new router will be new
BDR. Then the old BDR will send prune message to upstream routers. BDR. Then the old BDR will send prune message to upstream routers.
As a result, the BDR is the one which has the highest priority except As a result, the BDR is the one which has the highest priority except
DR. Once the DR is elected, the DR will not change until it fails or DR. Once the DR is elected, the DR will not change until it fails or
manually adjustment. After the DR and BDR are elected, the routers manually adjustment. After the DR and BDR are elected, the routers
in the network will store the address of DR and BDR. in the network will store the address of DR and BDR.
4.5. Sender side 4.6. Sender side
DR/BDR function also can be used in source side that multiple routers DR/BDR function also can be used in source side that multiple routers
and source is in same share-media network. The algorithm is the same and source is in same shared-media network. The algorithm is the
as the receiver side. Only the BDR need not build multicast tree same as the receiver side. Only the BDR need not build multicast
from downstream router. tree from downstream router.
5. Compatibility 5. Compatibility
If the LAN is a hybrid network that there are some routers which have If the LAN is a hybrid network that there are some routers which have
DR/BDR capability and the other routers which have not DR/BDR DR/BDR capability and the other routers which have not DR/BDR
capability. In order to avoid duplicated multicast flows in the LAN, capability. All the routers MAY go backward to use the algorithm
all the routers should go backward to use the algorithm defined in defined in [RFC7761].
[RFC4601] and [RFC7761].
6. Deployment suggestion 6. Deployment suggestion
If there are two and more routers on a share-media LAN, and the If there are two and more routers which is responsible for multicast
multicast services is sensitive to the lost of multicast packets, the flow forwarding on a shared-media LAN, and the multicast services is
function of DR and BDR defined in this document should be deployed. sensitive to the lost of multicast packets, the function of DR and
BDR defined in this document SHOULD be deployed.
7. Security Considerations 7. Security Considerations
For general PIM Security Considerations. For general PIM Security Considerations.
8. IANA Considerations 8. IANA Considerations
IANA is requested to allocate OptionTypes in TLVs of hello message. IANA is requested to allocate OptionType in TLVs of hello message.
Include DR and BDR. Include DR and BDR.
9. Normative References 9. Acknowledgements
The authors would like to thank Greg Mirsky for their valuable
comments and suggestions.
10. Normative References
[HRW] IEEE, "Using name-based mappings to increase hit rates", [HRW] IEEE, "Using name-based mappings to increase hit rates",
IEEE HRW, February 1998. IEEE HRW, February 1998.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>. <https://www.rfc-editor.org/info/rfc2328>.
[RFC2362] Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering, [RFC2362] Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering,
S., Handley, M., Jacobson, V., Liu, C., Sharma, P., and L. S., Handley, M., Jacobson, V., Liu, C., Sharma, P., and L.
Wei, "Protocol Independent Multicast-Sparse Mode (PIM-SM): Wei, "Protocol Independent Multicast-Sparse Mode (PIM-SM):
Protocol Specification", RFC 2362, DOI 10.17487/RFC2362, Protocol Specification", RFC 2362, DOI 10.17487/RFC2362,
June 1998, <https://www.rfc-editor.org/info/rfc2362>. June 1998, <https://www.rfc-editor.org/info/rfc2362>.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601,
DOI 10.17487/RFC4601, August 2006,
<https://www.rfc-editor.org/info/rfc4601>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>. 2016, <https://www.rfc-editor.org/info/rfc7761>.
Authors' Addresses Authors' Addresses
Zheng(Sandy) Zhang Zheng(Sandy) Zhang
ZTE Corporation ZTE Corporation
skipping to change at page 11, line 12 skipping to change at page 11, line 12
Email: zhang.zheng@zte.com.cn Email: zhang.zheng@zte.com.cn
Fangwei Hu Fangwei Hu
ZTE Corporation ZTE Corporation
No.889 Bibo Rd No.889 Bibo Rd
Shanghai Shanghai
China China
Email: hu.fangwei@zte.com.cn Email: hu.fangwei@zte.com.cn
BenChong Xu Benchong Xu
ZTE Corporation ZTE Corporation
No. 68 Zijinghua Road, Yuhuatai Distinct No. 68 Zijinghua Road, Yuhuatai Distinct
Nanjing Nanjing
China China
Email: xu.benchong@zte.com.cn Email: xu.benchong@zte.com.cn
Mankamana Prasad Mishra Mankamana Mishra
Cisco Systems Cisco Systems
821 Alder Drive, 821 Alder Drive,
MILPITAS, CALIFORNIA 95035 MILPITAS, CALIFORNIA 95035
UNITED STATES UNITED STATES
Email: mankamis@cisco.com Email: mankamis@cisco.com
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