IS-IS routing
NOTE: You must have an advanced features license to use IS-IS routing.
Intermediate System to Intermediate System Protocol (IS-IS) allows routing of ISO’s OSI protocol stack Connectionless Network Service (CLNS). IS-IS is an Interior Gateway Protocol (IGP) that is not intended to be used between Autonomous Systems (AS).
IS-IS is a link state protocol that is well-suited to smaller networks. It is in widespread use and has near universal support on routing hardware. It is quick to configure and works well if there are no redundant paths. However, IS-IS updates are sent out node-by-node, so it can be slow to find a path around network outages. IS-IS also lacks good authentication, can not choose routes based on different quality-of-service methods, and can create network loops if you are not careful. IS-IS uses Djikstra’s algorithm to find the best path, like OSPF.
While OSPF is more widely known, IS-IS is a viable alternative to OSPF in enterprise networks and ISP infrastructures, largely due to its native support for IPv6 and its nondisruptive methods for splitting, merging, migrating, and renumbering network areas.
This chapter covers the following topics:
Terminology
TLV: IS-IS uses type-length-value (TLV) parameters to carry information in Link-State PDUs (LSPs). The TLV field consists of one octet of type (T), one octet of length (L), and “L” octets of value (V).
Link-state PDU (LSP): The LSP contains information about each router in an area and its connected interfaces.
Complete sequence number PDU (CSNP): CSNPs contain a list of all LSPs in the current LSDB.
Authentication keychain: A keychain is a list of one or more authentication keys including the send and receive lifetimes for each key. Keys are used for authenticating routing packets only during the specified lifetimes.
Configuring IS-IS
The following is an example of an IS-IS configuration:
config router isis
set default-information-metric 60
config interface
edit "vlan100"
set circuit-type level-1
set priority-l1 80
set wide-metric-l1 200
next
edit "vlan102"
set circuit-type level-2
next
end
config net
edit 1
set net 49.0002.0000.0000.1048.00
next
end
set metric-style wide
config redistribute "connected"
set status enable
end
config redistribute "rip"
end
config redistribute "ospf"
end
config redistribute "bgp"
end
config redistribute "static"
end
end
Configuring BFD for IS-IS
You can use bidirectional forwarding detection (BFD) for the IS-IS routing protocol:
config router isis
config interface
edit <IS-IS interface name>
set bfd {enable| disable}
next
end
end
For example, if you want to enable BFD on vlan100:
config router isis
config interface
edit "vlan100"
set bfd enable
next
end
end
Checking the IS-IS configuration
Use the following commands to check your IS-IS configuration:
get router info isis interface
get router info isis route
get router info isis summary
get router info isis topology