| Notes on ISIS - General Protocol Information |
My notes on ISIS... Its general information picked from other websites too..
Topology
ISIS - General Protocol Info -
PDUs and Protocol Details
Hello - To discover neighbours. 3 way handshake is performed to form adjacency. Address-family should be same inorder to form adjacency.
L2 LSP - Link state - Exchange of route information : Link-state id, sequence number, area, interfaces, protocols supported, ipv4 internal reachability,[ if configured] ipv6 reachability.
CSNP - Complete Sequence Number
PSNP - Partial Sequence Number
| Category | Packet Type | Type Number |
| Hello | LAN Level-1 Hello | 15 |
| LAN Level-2 Hello | 16 | |
| Point-to-point Hello | 17 | |
| LSP | Level-1 LSP | 18 |
| Level-2 LSP | 20 | |
| SNP | Level-1 Complete SNP | 24 |
| Level-2 Complete SNP | 25 | |
| Level-1 Partial SNP | 26 | |
| Level-2 Partial SNP | 27 |
Padding - 08 type , length - ff - value can be zero or some pattern
Protocols supported - 81 , length - 02 , values - v4, v6 typically
Area Address - 01 , value - 04 bytes, values - something like 49.0001 kinds where 49 denotes private scheme in ISO standard
IPv4 Address - 84 , value - 4 - v4 Address of the interface where ISIS is enabled
IPv6 Address - e8 , value - 16 - v6 address of the interface
ISIS Neighbor - 06 , value - 6 bytes - MAC/SNAP address of the interface - typically the mac remains same for all the interface on a router
Extend ISIS reach-ability - 16 , value - list of all ISIS neighbors MAC address
Hostname - 7 , value - Name of the host - this is like DNS
LSP Entry in CSNP - 09 , Value - Contains max 240 bytes data of all the LSPs it knows
IS-Reachability - 12 , value - Neighbor sys-id address and its metric
IS-Reachability - 12 , value - Neighbor sys-id address and its metric
Flag Types
Partition repair -
Attached bits -
Overload bit - Doesn't take part in SPF calculation on other routers. As the router might not have all the routes/LSP. The router will be only included for connected routes.
IS type -value - 3 means - level2
| Troubleshooting Details |
CLIs
show isis neighbors : The adjacent neighbour info can be seen here. SNPA, local interface, state, hold-time , neighbors system-id
show isis summary : Details about the local systemid, internal, external preference, area which its part of, address-family support, is-type, lsdb
show isis interface : All the interfaces which are part of ISIS gets displayed here. Options help to find if specific interface is part of the ISIS or not. Default timers are not displayed here.
show isis database : All the database info - LSP Id, sequence number , age , flags gets displayed. With detail , we get to know about system id, routes reachability, neighbor info, interfaces , area etc
show ip route summary : Gives info on the number of ISIS routes
show ip route isis : All the routes related to ISIS is displayed
show run all interface : Provides info on all the default Timers for that specific interface
show isis summary : Details about the local systemid, internal, external preference, area which its part of, address-family support, is-type, lsdb
show isis interface : All the interfaces which are part of ISIS gets displayed here. Options help to find if specific interface is part of the ISIS or not. Default timers are not displayed here.
show isis database : All the database info - LSP Id, sequence number , age , flags gets displayed. With detail , we get to know about system id, routes reachability, neighbor info, interfaces , area etc
show ip route summary : Gives info on the number of ISIS routes
show ip route isis : All the routes related to ISIS is displayed
show run all interface : Provides info on all the default Timers for that specific interface
logging console 7 , terminal monitor - prints all the ISIS logs and also other logs . Currently the choice of only ISIS is not present
| Logging Info means |
Mar 12 00:16:48 sc213 Rib: %ISIS-4-ISIS_L2_DISCHG Intf: vlan12, Elected self as DIS, priority 64
Desc : The router has elected self for vlan 12 - Based on priority number or system-id
Mar 12 00:16:48 sc213 Rib: %ISIS-4-ISIS_ADJCHG:Neighbor State Change for SystemID 4455.6677.88c9 on vlan15 to UP
Desc : The Neigbhor systemid with 88c9 on vlan 15 has come up. With qt traces one can see the transitions of states - Like INIT to UP etc
Mar 12 00:16:49 sc213 Rib: %ISIS-4-ISIS_L2_DISCHG Intf: vlan53, Resigned as DIS priority 64, Elected sysid 4455.6677.88ef, priority 86
Desc : The EOS router resigned as DIS on vlan 53 and elected 88ef as DIS as it has higher priority
ISIS RECV: l2-psn source id doesn't match adjacencies
Desc : This is seen when source id inside l2-psn pdu system-id info does not match with already formed adjacency system-id info.
Mar 12 01:27:54 sc213 Rib: ISIS RECV: l2-csn source id doesn't match adjacencies
Desc : Same as above , but this is with CSN instead of PSN.
Desc : Same as above , but this is with CSN instead of PSN.
| Basic Configuration |
interface Port-Channel1
mtu 5000
switchport mode trunk
ip proxy-arp
ip address 200.8.8.1/24
arp timeout 60
isis enable 4294967294
isis priority 3
isis hello-interval 90
router isis 4294967294
net 48.0000.1111.ffff.00
is-type level-2
log-adjacency-changes
redistribute connected
redistribute static
address-family ipv4 unicast
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