Subject: Re: [Idr] BGP routes with color - EPE

From: "Swadesh Agrawal (swaagraw)" <[email-masked]>
Date: Tue, 5 Apr 2022 05:53:16 +0000

Hi Jeff,

Thanks for querying EPE aspects of BGP CAR.

Existing BGP LU based EPE operational model:
EPE forwarding action of directing the traffic on a link, set of links, peer or set of peers is executed on egress ASBR based on label in packet. This require to signal EPE label and encapsulate service flows with it. One of the well-known technique is to provide BGP LU routing extension to EPE. EPE link, links-set, peer and peer-set are presented as IP address (static config or EPE link peer address or peer loopback address) by ASBR with associated EPE label and advertised in BGP LU. These EPE BGP LU routes are propagated via RRs to ingress PEs with next hops as ASBR originating routes. To direct service flows to EPE, ASBR advertise service route with EPE IP address as next hops.

Example of routes on E1 which are learnt from ASBR E32
Service route   : V/v via I11-IP
EPE BGP LU route: I11-IP via E32, label 111
E32 is learnt through hop by hop BGP LU providing best effort path to E32.

   +-------------+      +-------------+      +-------------+          +
   |             |      |             |      |        +----|-------I11|     V/v
   |             |      |             |      |        |E32 |-------I21|
   |----+        |------|             |------|        +----|-------I31|     /
   | E1 |        |      |             |      |             |          |PEER \
   |----+        |      |             |      |        +----|-------I41|     W/w
   |             |------|             |------|        | E33|          |
   |             |      |             |      |        +----|-------I61|
   |  Domain 1   |      |   Domain 2  |      |   Domain 3  |          |
   +-------------+      +-------------+      +-------------+          +

Additionally, BGP CAR provide intent aware path to specific EPE BGP LU route when colored i.e. intent required by traffic to EPE link can be signaled in EPE BGP LU route by attaching color-EC. For example traffic directed to links I11,I21,I41 require purple treatment and to links I31,I61 require green treatment in transport.

Example of routes on E1 which are learnt from ASBR E32
V/v via I11-IP
W/w via I31-IP
I11-IP via E32, label 111, color-EC purple
I31-IP via E32, label 131, color-EC green
BGP CAR (E32, purple) creates intent-aware path to E32
BGP CAR (E32, green) creates intent-aware path to E32

Traffic bound to V/v is encapsulated with EPE label 111 and sent to purple BGP CAR LSP to E32. On E32 traffic exits through I11
Traffic bound to W/w is encapsulated with EPE label 131 and sent to green BGP CAR LSP to E32. On E32 traffic exits through I31.

Operator may advertise EPE route in BGP CAR and signal multiple intents for an EPE IP which recurses over different transport paths accordingly. Service prefixes are colored accordingly.

Further, EPE protection schemes are already well known and works in CAR
- Local protection via alternate link on E32 i.e. I11 alternate link would be I21
- Fallback to IP forwarding. Lookup of service routes learnt from PEER provide alternate path when one of the links fail.
- Rerouting traffic through alternate router E33. This backup path satisfies intent between E32 and E33. E33 can be in another domain as well.

There are additional possible use-cases and simplification BGP-CAR can provide with respect to representing EPE link, set of links, peer and peer-set in routing.

Regards
Swadesh

On 3/22/22, 12:46 PM, "Idr on behalf of Jeffrey Haas" <[email-masked] on behalf of [email-masked]> wrote:

    Authors,

    Ben Maddison raised an interesting scenario at the end of the IDR session

    that may be helpful in discussing route propagation properties for the

    proposals: Egress Peer Engineering (EPE).

    Please supply an example of your proposal being used for EPE.

    Thanks!

    -- Jeff

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