IS-IS

                                             ┌──────┐
                                             │ L1   │
                                             └───┬──┘
                                                 │
┌──────┐     ┌──────┐        ┌──────┐        ┌───┴──┐     ┌─────┐
│  L1  ├─────┤ L1L2 ├────────┤  L2  ├────────┤ L1L2 ├─────┤ L1  │
└───┬──┘     └───┬──┘        └──────┘        └───┬──┘     └─────┘
    │            └──────┐                  ┌─────┘
┌───┴──┐             ┌──┴───┐          ┌───┴──┐
│  L1  │             │  L2  │──────────┤  L2  │
└──────┘             └──────┘          └──────┘

Topologies

Single Topology

All Routed Protocols must be configured on all enabled interfaces
e.g. v4 and v6 on all interfaces.

Multi-Topology

Requires wide metrics
Links can have different costs
Some interfaces can be v4, others can be v6, others can be both
IOS-XR default to MT

Addressing scheme

packet-beta
0-7: "AFI"
8-23: "Area ID"
24-71: "System ID"
72-79: "SEL"

AFI

Authority and Format Identifier - 1 byte
49 means local authority, and hexadecimal (binary is encoded).

Area ID

Variable, and … includes the AFI

System ID

6 bytes, can fit a MAC address or a v4 address
Must be unique in an area for L1
Must be unique in a domain for L2

SEL

Selector - 1 byte
This is always 00 to mean router

Example

net 49.0001.0000.0A00.0001.00

So long as the NSAP is unique, its OK because we aren’t routing CLNS.

Priority is used for the CLNS election. Circuit ID, who won the election

Etc

ISIS does not ride IP, it rides CLNS. To do Multipoint NBMA you need to include CLNS resolution.

L1 areas must match

Supported Network Types

Point-to-point
Broadcast

IS-IS narrow

The Cisco default link cost is 10.

These are the limits:

63 per link
1 023 per path

IS-IS wide

16 777 215 per link
4 294 967 295 per path

Cisco’s implementation of the wide metric uses the bits ISO set aside for delay, expense and error.

Config

Enable wide metrics:

metric-style wide

Metric transition commands

Used when migrating from narrow to wide without a hard cutover:

Command	Behavior
`metric-style transition`	Advertises both narrow and wide TLVs simultaneously
`metric-style narrow transition`	Transitioning — still advertising narrow (old)
`metric-style wide transition`	Transitioning — now advertising wide (new)

IS-IS authentication

Plaintext
- Link, Area, or Domain
  - Link is between routers
  - Area is every router must have a matching password
  - L2 and L1/L2 router use domain authentication.

Notes

Default route injected via route-map.

Config

IS-IS checks for sanity, if only one protocol is being shared over IS-IS … adding a second one will break adjacencies.

A workaround is to disable the adjacency check.

IPv6 not enabled on neighbor

router isis
  address family ipv6
    no adjacency check

Single topology v6

interface Gi1
  ip address 10.0.0.1 255.255.255.0
  ipv6 address fe80::1 link-local
  !
  ! This means only send IPv6 TLVs
  !
  ipv6 router isis
!
! This is single topology
! 
router isis
  net 49.0001.1111.1111.1111.00

Multi topology v6

Requires wide metrics

interface Gi1
  ip address 10.0.0.1 255.255.255.0
  ipv6 address fe80::1 link-local
  ip router isis
  ipv6 router isis
  isis ipv6 metric 1234
!
router isis
  net 49.0001.1111.1111.1111.00
  metric-style wide
  address-family ipv6
    multi-topology

References

RFC 5120: M-ISIS: MT Routing in IS-IS | RFC Editor

RFC 1195: Use of OSI IS-IS for routing in TCP/IP and dual environments | RFC Editor

RFC 5308: Routing IPv6 with IS-IS | RFC Editor

Cisco Live - Deploying IPv6 Routing Protocols - Peter Palúch - BRKIPV-2418

ISO/IEC 10589:2002 - IT — Telecommunications and information exchange between systems

ISO/IEC 8348:2002 - Information technology — Open Systems Interconnection — Network service definition

Keyboard shortcuts