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IS-IS¶
IS-IS is a link-state interior gateway routing protocol which is described in ISO10589, RFC 1195, RFC 5308. Like OSPF, IS-IS runs the Dijkstra shortest-path first (SPF) algorithm to create a database of the network’s topology and, from that database, to determine the best (that is, shortest) path to a destination. The routers exchange topology information with their nearest neighbors. IS-IS runs directly on the data link layer (Layer 2). IS-IS addresses are called NETs and can be 8 to 20 bytes long, but are generally 10 bytes long.
For example NET
49.0001.1921.6800.1002.00
The IS-IS address consists of three parts:
- AFI
49The AFI value 49 is what IS-IS uses for private addressing.- Area identifier:
0001IS-IS area number (Area1)- System identifier:
1921.6800.1002For system idetifier we recommend to use IP address or MAC address of the router.- NET selector:
00Must always be 00, to indicate “this system”.
General Configuration¶
This command enables the ISIS process by specifying the ISIS domain with ‘name’. ISIS implementation does not yet support multiple ISIS processes but you must specify the name of ISIS process. This commad also sets network entity title (NET) provided in ISO format.
This command activates ISIS adjacency on this interface. Note that the name of ISIS instance must be the same as the one used to configure the ISIS process.
This command enables support for dynamic hostname. Dynamic hostname mapping determined as described in RFC 2763, Dynamic Hostname Exchange Mechanism for IS-IS.
This command defines the ISIS router behavior:
level-1 Act as a station router only. level-1-2 Act as both a station router and an area router. level-2-only Act as an area router only.
This command configures the maximum size of generated LSPs, in bytes. The size range is 128 to 4352.
This command sets old-style (ISO 10589) or new-style packet formats:
narrow Use old style of TLVs with narrow metric. transition Send and accept both styles of TLVs during transition. wide Use new style of TLVs to carry wider metric.
This command enables RFC 6232 purge originator identification. Enable purge originator identification (POI) by adding the type, length and value (TLV) with the Intermediate System (IS) identification to the LSPs that do not contain POI information. If an IS generates a purge, VyOS adds this TLV with the system ID of the IS to the purge.
This command sets ATT bit to 1 in Level1 LSPs. It is described in RFC 3787.
This command sets overload bit to avoid any transit traffic through this router. It is described in RFC 3787.
This command will generate a default-route in L1 database.
Interfaces Configuration¶
This command specifies circuit type for interface:
level-1 Level-1 only adjacencies are formed. level-1-2 Level-1-2 adjacencies are formed level-2-only Level-2 only adjacencies are formed
This command sets hello interval in seconds on a given interface. The range is 1 to 600.
This command sets multiplier for hello holding time on a given interface. The range is 2 to 100.
This command configures padding on hello packets to accommodate asymmetrical maximum transfer units (MTUs) from different hosts as described in RFC 3719. This helps to prevent a premature adjacency Up state when one routing device’s MTU does not meet the requirements to establish the adjacency.
This command set default metric for circuit. The metric range is 1 to 16777215 (Max value depend if metric support narrow or wide value).
This command specifies network type to ‘Point-to-Point’. The default network type is broadcast.
This command configures the passive mode for this interface.
This command configures the authentication password for the interface.
This command sets priority for the interface for DIS election. The priority range is 0 to 127.
This command sets PSNP interval in seconds. The interval range is 0 to 127.
This command disables Three-Way Handshake for P2P adjacencies which described in RFC 5303. Three-Way Handshake is enabled by default.
Redistribution Configuration¶
This command redistributes routing information from the given route source into the ISIS database as Level-1. There are six modes available for route source: bgp, connected, kernel, ospf, rip, static.
This command redistributes routing information from the given route source into the ISIS database as Level-2. There are six modes available for route source: bgp, connected, kernel, ospf, rip, static.
This command specifies metric for redistributed routes from the given route source. There are six modes available for route source: bgp, connected, kernel, ospf, rip, static. The metric range is 1 to 16777215.
Timers Configuration¶
This command sets minimum interval in seconds between regenerating same LSP. The interval range is 1 to 120.
This command sets LSP refresh interval in seconds. IS-IS generates LSPs when the state of a link changes. However, to ensure that routing databases on all routers remain converged, LSPs in stable networks are generated on a regular basis even though there has been no change to the state of the links. The interval range is 1 to 65235. The default value is 900 seconds.
This command sets LSP maximum LSP lifetime in seconds. The interval range is 350 to 65535. LSPs remain in a database for 1200 seconds by default. If they are not refreshed by that time, they are deleted. You can change the LSP refresh interval or the LSP lifetime. The LSP refresh interval should be less than the LSP lifetime or else LSPs will time out before they are refreshed.
This command sets minimum interval between consecutive SPF calculations in seconds.The interval range is 1 to 120.
This commands specifies the Finite State Machine (FSM) intended to control the timing of the execution of SPF calculations in response to IGP events. The process described in RFC 8405.
Configuration Example¶
Simple IS-IS configuration using 2 nodes and redistributing connected interfaces.
Node 1:
set interfaces dummy dum0 address '203.0.113.1/24'
set interfaces ethernet eth1 address '192.0.2.1/24'
set policy prefix-list EXPORT-ISIS rule 10 action 'permit'
set policy prefix-list EXPORT-ISIS rule 10 prefix '203.0.113.0/24'
set policy route-map EXPORT-ISIS rule 10 action 'permit'
set policy route-map EXPORT-ISIS rule 10 match ip address prefix-list 'EXPORT-ISIS'
set protocols isis FOO interface eth1
set protocols isis FOO net '49.0001.1921.6800.1002.00'
set protocols isis FOO redistribute ipv4 connected level-2 route-map 'EXPORT-ISIS'
Node 2:
set interfaces ethernet eth1 address '192.0.2.2/24'
set protocols isis FOO interface eth1
set protocols isis FOO net '49.0001.1921.6800.2002.00'
Show ip routes on Node2:
vyos@r2:~$ show ip route isis
Codes: K - kernel route, C - connected, S - static, R - RIP,
O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
F - PBR, f - OpenFabric,
> - selected route, * - FIB route, q - queued route, r - rejected route
I 203.0.113.0/24 [115/10] via 192.0.2.1, eth1, 00:03:42