Closed ZoeyFahner-Arista closed 6 months ago
After speaking with @ClausHolbechArista it makes sense to keep the IS-IS system_id
format selection knob as a global IS-IS parameter, similar to how we configure the overlay options for RD / RT, etc.
Additionally since this is a more resilient method of ensuring IS-IS system_id
uniqueness it may be made the default format for AVD 5.0 as long as migration notes are included that the behavior is changing on the major version release.
eos_designs
Top-Level Key
# Selection of either node ID or Underlay Loopback (Loopback0) to create the IS-IS `system_id` field
isis_system_id_format: <str; "id" | "underlay_loopback"; default="underlay_loopback">
Enhancement summary
Currently AVD utilizes the
node id
of the element to generate the IS-IS system-id field. In some situations where multiple node groups are utilized this can result in a duplication of thesystem-id
field which will cause IS-IS to malfunction. This issue requests a knob to construct the IS-ISsystem-id
field based on the router's Loopback0 underlay IP, guaranteeing global uniqueness within the fabric.Which component of AVD is impacted
eos_designs
Use case example
Demonstration of Issue
Consider the following AVD configuration where the customer has requested a subnet per site for Underlay Loopback generation. Both nodes utilize an ID of 1 to obtain the first loopback in each group.
Which results in both
FIZZ-01
andBUZZ-01
getting an identical IS-IS NET of49.0001.0000.0000.0001.00
, which will not operate correctly. However, both routers do have unique underlay Loopback addresses (192.168.203.1
and192.168.204.1
).Describe the solution you would like
Loopback to IS-IS System-ID Conversion
Many service providers encode the underlay Loopback IP address into the IS-IS
system-id
field the following way:.
), leaving a string of integerssystem-id
delimiter (.
) every four digitsExamples
Shown using an
isis_system_id_prefix
of49.0001
and the defaultNSEL
of00
.Add the following new option to the IS-IS dictionary within the AVD
eos_designs
to allow selection of the Underlay Loopback. Here is a proposed diff of the schema:Describe alternatives you have considered
Right now we can work around the limitation using structured configuration under each node to overwrite the auto-generated IS-IS
system-id
(while also having to keep track of thenet-id
manually):Overriding the
isis_system_id_prefix
on a per-group basis to ensure a globally unique IS-ISnet-id
is not a solution since it would create different IS-IS network areas and is an invalid configuration for the target topology.Additional context
Caveats
Care must be taken that the knob remains defaulted to
id
so that existing customers utilizing AVD do not have a reconfiguration of the IS-IS NET ID.Contributing Guide