draft-ietf-isis-omp-00.txt   draft-ietf-isis-omp-01.txt 
Internet Engineering Task Force Curtis Villamizar Internet Engineering Task Force Curtis Villamizar
INTERNET-DRAFT ANS INTERNET-DRAFT ANS
draft-ietf-isis-omp-00 Tony Li draft-ietf-isis-omp-01 Tony Li
Juniper Juniper
January 12, 1999 February 22, 1999
IS-IS Optimized Multipath (ISIS-OMP) IS-IS Optimized Multipath (ISIS-OMP)
Status of this Memo Status of this Memo
This document is an Internet--Draft. Internet--Drafts are working This document is an Internet-Draft and is in full conformance with all
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Copyright (C) The Internet Society (February 22, 1999). All Rights
Reserved.
Abstract Abstract
IS--IS may form multiple equal cost paths between points. This is IS--IS may form multiple equal cost paths between points. This is
true of any link state protocol. In the absence of any explicit sup- true of any link state protocol. In the absence of any explicit sup-
port to take advantage of this, a path may be chosen arbitrarily. port to take advantage of this, a path may be chosen arbitrarily.
Techniques have been utilized to divide traffic somewhat evenly among Techniques have been utilized to divide traffic somewhat evenly among
the available paths. These techniques have been referred to as Equal the available paths. These techniques have been referred to as Equal
Cost Multipath (ECMP). An unequal division of traffic among the avail- Cost Multipath (ECMP). An unequal division of traffic among the avail-
able paths is generally preferable. Routers generally have no knowl- able paths is generally preferable. Routers generally have no knowl-
edge of traffic loading on distant links and therefore have no basis edge of traffic loading on distant links and therefore have no basis
to optimize the allocation of traffic. to optimize the allocation of traffic.
Optimized Mulitpath is a extension to IS--IS, utilizing additional Optimized Mulitpath is a extension to IS--IS, utilizing additional
Type/Length/Value (TLV) tuples to distribute loading information. An Type/Length/Value (TLV) tuples to distribute loading information. An
algorithm to adjust forwarding, gradually enough to insure stability algorithm to adjust forwarding, gradually enough to insure stability
yet provide reasonably fast adjustment when needed, is provided in the yet provide reasonably fast adjustment when needed, is provided in the
related document OSPF--OMP [5]. The IS--IS encapsulation and minor related document OSPF--OMP [6]. The IS--IS encapsulation and minor
differences in the dynamics of ISIS--OMP relative to OSPF--OMP are differences in the dynamics of ISIS--OMP relative to OSPF--OMP are
described here. described here.
1 Overview 1 Overview
IS--IS is OSI link state routing protocol [2]. OSPF is a link state IS--IS is OSI link state routing protocol [2]. OSPF is a link state
routing protocol defined within the IETF process [3]. IS--IS can also routing protocol defined within the IETF process [4]. IS--IS can also
be used as an IP interior gateway protocol (IGP) much as OSPF is used be used as an IP interior gateway protocol (IGP) much as OSPF is used
[1]. [1].
Networks are often heavily loaded. Topologies often evolve to include Networks are often heavily loaded. Topologies often evolve to include
multiple paths. Multiple paths may be initially designed to provide multiple paths. Multiple paths may be initially designed to provide
redundancy but also result from incremental addition of circuits to redundancy but also result from incremental addition of circuits to
accommodate traffic growth. The redundant paths provide a potential accommodate traffic growth. The redundant paths provide a potential
to distribute traffic loading and reduce congestion. Optimized Mulit- to distribute traffic loading and reduce congestion. Optimized Mulit-
path (OMP) provides a means for a link state protocol such as IS--IS path (OMP) provides a means for a link state protocol such as IS--IS
or OSPF to make better use of this potential to distribute loading. or OSPF to make better use of this potential to distribute loading.
Please refer to [5] for a more complete introduction to OMP. Please refer to [6] for a more complete introduction to OMP.
2 Differences Between ISIS--OMP and OSPF--OMP 2 Differences Between ISIS--OMP and OSPF--OMP
Both IS--IS and OSPF are link state protocols. The technique of equal Both IS--IS and OSPF are link state protocols. The technique of equal
cost multipath (ECMP) routing is formally defined in OSPF [3] but has cost multipath (ECMP) routing is formally defined in OSPF [4] but has
also been applied to IS--IS implementations. Because these routing also been applied to IS--IS implementations. Because these routing
protocols are quite similar, application of OMP techniques is very protocols are quite similar, application of OMP techniques is very
similar. similar.
Differences between OSPF and IS--IS that impact OMP are: Differences between OSPF and IS--IS that impact OMP are:
1. The encapsulation of IS--IS link state information is different so 1. The encapsulation of IS--IS link state information is different so
the encapsulation of link loading information will be different. the encapsulation of link loading information will be different.
2. IS--IS link state information is flooded in no more than 256 LSPDU 2. IS--IS link state information is flooded in no more than 256 LSPDU
skipping to change at page 3, line 10 skipping to change at page 3, line 13
3. IS--IS Level 2 routing differs from OSPF inter--area routing. 3. IS--IS Level 2 routing differs from OSPF inter--area routing.
4. IS--IS handling of external routes in Level 2 differs from OSPF 4. IS--IS handling of external routes in Level 2 differs from OSPF
handling of external routes. handling of external routes.
2.1 Encapsulation 2.1 Encapsulation
IS--IS packs link state information in Type/Length/Value tuples. The IS--IS packs link state information in Type/Length/Value tuples. The
type and length are one byte each. The length is a unsigned byte pro- type and length are one byte each. The length is a unsigned byte pro-
viding the length in bytes of the Value portion of the tuple. The viding the length in bytes of the Value portion of the tuple. The
``extended IS reachability TLV'' is defined by Li as type 22 [?].1 ``extended IS reachability TLV'' is defined by Li as type 22 [3].
Subtypes of this TLV include the following: Subtypes of this TLV include the following, however if there are any
differences in a descendant to [3], consider that list to be authori-
tative.
IPv4 interface address subtype 6, length 4 IPv4 interface address subtype 6, length 4
IPv4 neighbor address subtype 8, length 4 IPv4 neighbor address subtype 8, length 4
Maximum (out) link bandwidth subtype 9, length 4 Maximum (out) link bandwidth subtype 9, length 4
Current (out) bandwidth usage subtype 12, length 4 Current (out) bandwidth usage subtype 12, length 4
Maximum inbound bandwidth usage subtype 15, length 4 Maximum inbound bandwidth usage subtype 15, length 4
Outbound fractional packet loss subtype 17, length 4 Outbound fractional packet loss subtype 17, length 4
Inbound fractional packet loss subtype 18, length 4 Inbound fractional packet loss subtype 18, length 4
Maximum inbound link bandwidth subtype 19, length 4 Maximum inbound link bandwidth subtype 19, length 4
skipping to change at page 3, line 26 skipping to change at page 3, line 31
Current (out) bandwidth usage subtype 12, length 4 Current (out) bandwidth usage subtype 12, length 4
Maximum inbound bandwidth usage subtype 15, length 4 Maximum inbound bandwidth usage subtype 15, length 4
Outbound fractional packet loss subtype 17, length 4 Outbound fractional packet loss subtype 17, length 4
Inbound fractional packet loss subtype 18, length 4 Inbound fractional packet loss subtype 18, length 4
Maximum inbound link bandwidth subtype 19, length 4 Maximum inbound link bandwidth subtype 19, length 4
The value part these TLV tuples are described below: The value part these TLV tuples are described below:
IPv4 interface address, subtype 6, length 4 This is the IPv4 address IPv4 interface address, subtype 6, length 4 This is the IPv4 address
of the near end of the interface. of the near end of the interface.
IPv4 neighbor address, subtype 8, length 4 This is the IPv4 address IPv4 neighbor address, subtype 8, length 4 This is the IPv4 address
of the far end of a point to point interface. of the far end of a point to point interface.
Maximum (out) link bandwidth, subtype 9, length 4 This is an IEEE 754 Maximum (out) link bandwidth, subtype 9, length 4 This is an IEEE 754
format 32 bit floating point number representing the bandwidth of format 32 bit floating point number representing the bandwidth of
the interface in bytes per second. See subtype 19. the interface in bytes per second. See subtype 19.
Current (out) bandwidth usage, subtype 12, length 4 This is an IEEE Current (out) bandwidth usage, subtype 12, length 4 This is an IEEE
754 format 32 bit floating point number representing the outbound 754 format 32 bit floating point number representing the outbound
link utilization of the interface in bytes per second. link utilization of the interface in bytes per second.
Maximum inbound bandwidth usage, subtype 15, length 4 This is an IEEE Maximum inbound bandwidth usage, subtype 15, length 4 This is an IEEE
754 format 32 bit floating point number representing the inbound 754 format 32 bit floating point number representing the inbound
link utilization of the interface in bytes per second. link utilization of the interface in bytes per second.
Outbound fractional packet loss, subtype 17, length 4 This is an IEEE Outbound fractional packet loss, subtype 17, length 4 This is an IEEE
754 format 32 bit floating point number representing the ratio of 754 format 32 bit floating point number representing the ratio of
lost outbound packets (generally lost due to queueing drop) to to- lost outbound packets (generally lost due to queueing drop) to to-
tal outbound packets. tal outbound packets.
Inbound fractional packet loss, subtype 18, length 4 This is an IEEE Inbound fractional packet loss, subtype 18, length 4 This is an IEEE
754 format 32 bit floating point number representing the ratio of 754 format 32 bit floating point number representing the ratio of
___lost_inbound_packets_to_total_inbound packets. lost inbound packets to total inbound packets.
1a draft is expected describing a set of IS--IS extensions in a
type 22 TLV when the IETF has formed an IS--IS WG
Maximum inbound link bandwidth, subtype 19, length 4 This is an IEEE Maximum inbound link bandwidth, subtype 19, length 4 This is an IEEE
754 format 32 bit floating point number representing the inbound 754 format 32 bit floating point number representing the inbound
bandwidth of the interface in bytes per second. If this subtype is bandwidth of the interface in bytes per second. If this subtype is
not present the link is assumed to be symmetric and the value given not present the link is assumed to be symmetric and the value given
in a type 9 subtype TLV is used as both the inbound and outbound in a type 9 subtype TLV is used as both the inbound and outbound
bandwidth of the interface. bandwidth of the interface.
2.2 Flooding 2.2 Flooding
OSPF link state information is flooded in individual Link State At- OSPF link state information is flooded in individual Link State At-
tributes that may be independently flooded or packed for efficiency. tributes that may be independently flooded or packed for efficiency.
IS--IS considers the entire link state database to be somewhat of an IS--IS considers the entire link state database to be somewhat of an
atomic entity expressed as the Link State Protocol Data Unit (LSPDU). atomic entity expressed as the Link State Protocol Data Unit (LSPDU).
The LSPDU can be flooded in up to 256 LSPDU fragments. When a frag- The LSPDU can be flooded in up to 256 LSPDU fragments. When a frag-
ment is reflooded with a change, all link information in that fragment ment is reflooded with a change, all link information in that fragment
must be reflooded. Link loading information which otherwise might not must be reflooded. Link loading information which otherwise might not
be flooded for some time will be updated. This is expected to have be flooded for some time will be updated. This is expected to have
minimal impact on the dynamics of the OMP algorithm. minimal impact on the dynamics of the OMP algorithm.
An algorithm for filtering raw counter values and determining when An algorithm for filtering raw counter values and determining when
to flood is provided in [5] stated quite concisely in the appendices. to flood is provided in [6] stated quite concisely in the appendices.
The IS--IS algorithm differs only in that link loading may be flooded The IS--IS algorithm differs only in that link loading may be flooded
at times simply because the link resides in an LSPDU fragment that at times simply because the link resides in an LSPDU fragment that
must be reflooded due to a loading change in another link. must be reflooded due to a loading change in another link.
2.3 Relaxing Best Path Criteria 2.3 Relaxing Best Path Criteria
The IS--IS best path metric criteria can be relaxed just as the best The IS--IS best path metric criteria can be relaxed just as the best
path criteria is relaxed in OSPF--OMP. The same restrictions apply. path criteria is relaxed in OSPF--OMP. The same restrictions apply.
In no circumstance should traffic toward an exit point with equal In no circumstance should traffic toward an exit point with equal
external cost or toward an internal destination be sent to an neigh- external cost or toward an internal destination be sent to an neigh-
skipping to change at page 5, line 44 skipping to change at page 5, line 47
In IS--IS, as specified only Level 2 routers may carry external rout- In IS--IS, as specified only Level 2 routers may carry external rout-
ing information. Level 1 routers are expected to route only to des- ing information. Level 1 routers are expected to route only to des-
tinations in their own area or to the nearest Level 2 router. The tinations in their own area or to the nearest Level 2 router. The
Level 2 routers have complete information and can route the packet Level 2 routers have complete information and can route the packet
toward the correct area or to a router advertising the external route. toward the correct area or to a router advertising the external route.
In practice this is rarely an issue and implementations allow this In practice this is rarely an issue and implementations allow this
aspect of the specification to be violated. aspect of the specification to be violated.
Generally ISIS is not used to carry exterior routing information. Generally ISIS is not used to carry exterior routing information.
Instead, a separate exterior gateway protocol is used, specifically Instead, a separate exterior gateway protocol is used, specifically
BGP--4 [4]. When BGP--4 is used to carry external routes within an AS BGP--4 [5]. When BGP--4 is used to carry external routes within an AS
(this is referred to as Internal BGP or IBGP), IS--IS is used strictly (this is referred to as Internal BGP or IBGP), IS--IS is used strictly
as an Interior Gateway Protocol (IGP). IBGP learned routes contain a as an Interior Gateway Protocol (IGP). IBGP learned routes contain a
NEXT_HOP attribute which contains an address that is reachable via the NEXT_HOP attribute which contains an address that is reachable via the
IGP but often not directly connected. This is commonly referred to as IGP but often not directly connected. This is commonly referred to as
a recursive route lookup. When the IS--IS learned IGP route is used, a recursive route lookup. When the IS--IS learned IGP route is used,
the load balancing used to reach the IGP destination specified by the the load balancing used to reach the IGP destination specified by the
BGP NEXT_HOP is applied to the traffic routed toward that intermediate BGP NEXT_HOP is applied to the traffic routed toward that intermediate
destination. destination.
Some relaxation of routing criteria is possible to improve load bal- Some relaxation of routing criteria is possible to improve load bal-
skipping to change at page 6, line 47 skipping to change at page 7, line 5
vironments. Technical Report RFC 1195, Internet Engineering Task vironments. Technical Report RFC 1195, Internet Engineering Task
Force, 1990. ftp://ftp.isi.edu/in-notes/rfc1195.txt. Force, 1990. ftp://ftp.isi.edu/in-notes/rfc1195.txt.
[2] ISO/IEC. Iso/iec 10589 - information processing systems - [2] ISO/IEC. Iso/iec 10589 - information processing systems -
telecommunications and information exchange between systems - telecommunications and information exchange between systems -
intermediate system to intermediate system intra-domain routing intermediate system to intermediate system intra-domain routing
information exchange protocol for use in conjunction with the information exchange protocol for use in conjunction with the
protocol for providing the connectionless-mode network service protocol for providing the connectionless-mode network service
(iso 8473). Technical report, International Organization for (iso 8473). Technical report, International Organization for
Standardization, 1992. ftp://merit.edu/pub/iso/iso10589.ps.gz. Standardization, 1992. ftp://merit.edu/pub/iso/iso10589.ps.gz.
[3] J. Moy. Ospf version 2. Technical Report RFC 2328, Internet Engi- [3] Tony Li and Henk Smit. Is-is extensions for traffic en-
neering Task Force, 1998. ftp://ftp.isi.edu/in-notes/rfc2328.txt. gineering. Internet Draft (Work in Progress) draft-ietf-
isis-traffic-00, Internet Engineering Task Force, 2 1999.
ftp://ftp.isi.edu/internet-drafts/draft-ietf-isis-traffic-00.txt.
[4] Y. Rekhter and T. Li. A border gateway protocol 4 (bgp-4). Tech- [4] J. Moy. Ospf version 2. Technical Report RFC 2328, Internet Engi-
neering Task Force, 1998. ftp://ftp.isi.edu/in-notes/rfc2328.txt.
[5] Y. Rekhter and T. Li. A border gateway protocol 4 (bgp-4). Tech-
nical Report RFC 1771, Internet Engineering Task Force, 1995. nical Report RFC 1771, Internet Engineering Task Force, 1995.
ftp://ftp.isi.edu/in-notes/rfc1771.txt. ftp://ftp.isi.edu/in-notes/rfc1771.txt.
[5] Curtis Villamizar. Ospf optimized multipath (ospf-omp). Inter- [6] Curtis Villamizar. Ospf optimized multipath (ospf-omp). Inter-
net Draft (Work in Progress) draft-ietf-ospf-omp-01, Internet net Draft (Work in Progress) draft-ietf-ospf-omp-01, Internet
Engineering Task Force, 10 1998. ftp://ftp.isi.edu/internet- Engineering Task Force, 10 1998. ftp://ftp.isi.edu/internet-
drafts/draft-ietf-ospf-omp-01.txt. drafts/draft-ietf-ospf-omp-01.txt.
Security Considerations Security Considerations
In deployments which use a strong IS--IS authentication method, and In deployments which use a strong IS--IS authentication method, and
require signatures on LSP fragments from the originating router, no require signatures on LSP fragments from the originating router, no
leveraging of a partial compromise beyond a localized disruption of leveraging of a partial compromise beyond a localized disruption of
service is possible. In deployments which use a strong IS--IS authen- service is possible. In deployments which use a strong IS--IS authen-
skipping to change at page 7, line 39 skipping to change at page 7, line 46
Author's Addresses Author's Addresses
Curtis Villamizar Tony Li Curtis Villamizar Tony Li
ANS Juniper Networks ANS Juniper Networks
<curtis@ans.net> <tli@juniper.net> <curtis@ans.net> <tli@juniper.net>
A Configuration Options A Configuration Options
Many of the capabilities must be configurable. The ability to enable Many of the capabilities must be configurable. The ability to enable
and disable capability subsets is needed. Many parameters used by the and disable capability subsets is needed. Many parameters used by the
algorithm should also be configurable. Please refer to [5] for pa- algorithm should also be configurable. Please refer to [6] for pa-
rameter settings. ISIS--OMP differs from OSPF--OMP in the capability rameter settings. ISIS--OMP differs from OSPF--OMP in the capability
subsets. subsets.
A.1 Capability Subsets A.1 Capability Subsets
There should at least be the ability to enabled and disabled the fol- There should at least be the ability to enabled and disabled the fol-
lowing. lowing.
default description of capability default description of capability
ON Flooding any loading information ON Flooding any loading information
 End of changes. 

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