Remove RT-1.26.3 static route preference #3664
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Pull Request Functional Test Report for #3664 / ed9ef93Virtual Devices
Hardware Devices
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Pull Request Test Coverage Report for Build 12424046725Details
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Why is the functionality not correct? Could you eleborate? |
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This is an incorrect use of preference. Preference is defined as selecting the desired route between different protocols. (for example: static vs. BGP vs. ISIS). Preference is not defined (in OC) as selection criteria between two routes in the same protocol. |
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@dplore In case management HA CPN topology, we have default route being received by BGP and we have a backup static default route as well. The design is to use the iBGP default route as more preferred route over the static route. Hence the AD of static route is modified. Please refer to b/373412048 for recent CPN HA design change as well as 'https://docs.google.com/document/d/1l9KsbhgzLb3lXgxsledrqktYIam5TBoMqvy5em3m5hU/edit?tab=t.0#heading=h.jzghbleb96qw ' where option#1 was finalized. |
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We should use a next hop with a higher metric to get the backup static
route behavior.
@rszarecki for any additional comments
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@dplore but AD is the first things that gets looked into for route selection (When the prefix is received from multiple protocols). |
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If I understand correctly we have one or more default BGP routes AND static
default route with single next-hop. The intention is that static route
serves as backup - so-stalled floating static.
In this case preference of static should be modified to be > then BGP.
Probably 220 will just work.
We use above in MVC management HA.
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Rafal Szarecki
On Mon, Dec 30, 2024 at 11:56 Swetha-haridasula ***@***.***> wrote:
@dplore <https://github.com/dplore> but AD is the first things that gets
looked into for route selection (When the prefix is received from multiple
protocols).
The default route is available via static and iBGP. If we did not modify
the AD then static route is choosen even if the metric of the route is
modified here.
Requested ***@***.*** also inputs in bug as he knows the CPN
design here
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No.
First think is to select best route in each protocol independently, using
protocols specific attributes - locPref, as-path Len, med for BGP. SPF
path metric for Isis, next-hop metric for static.
Then AD is the only metric used to select between protocols.
IMHO the OpenConfig model for static is ambiguous, because it allows 2
attributes - metric and preference per each next-hop.
W/o standardization which one is more important.
And inconsistent with other protocols, which do not allow for distinct AD
per path/next-hop or even per prefix.
IMHO preference/AD should be attribute of prefix, not of next-hop. This
will solve ambiguity, while reducing flexibility a bit. Still more flexible
than other protocols.
Or maybe we need better describe use and behavior of static’preference as.
- not used to select best among static route next-hops
- carried by selected best static route to cross-protocol comparison of
per-protocol best routes which selects system-best-and-active route.
…--------------
Rafal Szarecki
On Mon, Dec 30, 2024 at 11:56 Swetha-haridasula ***@***.***> wrote:
@dplore <https://github.com/dplore> but AD is the first things that gets
looked into for route selection (When the prefix is received from multiple
protocols).
The default route is available via static and iBGP. If we did not modify
the AD then static route is choosen even if the metric of the route is
modified here.
Requested ***@***.*** also inputs in bug as he knows the CPN
design here
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@rszarecki . Yes I agree of your opinion of better describe use and behavior of static’preference as' carried by selected best static route to cross-protocol comparison of per-protocol best routes which selects system-best-and-active route' . But the usage of preference/AD in static route for management HA is necessary. @dplore , please let me know of your thoughts |
The functionality in the README is not correct and the feature as stated is not required.