Hi Iwase,
exactly. When there are more BGP speakers on the same segment (or LAN), I
expect that none of them changes the next hop, if the BGP announcement is being
forwarded to a BGP speaker in the same segment (or LAN). This is what other BGP
implementations (e.g. Quagga) do. So, I expected Ryu did the same, namely it
did not update the NEXT_HOP attribute as well.
Thanks,
Gabriele
________________________________
Da: Iwase Yusuke <iwase.yusu...@gmail.com>
Inviato: lunedì 25 dicembre 2017 01:49
A: g...@lospoto.it
Cc: ryu-devel@lists.sourceforge.net
Oggetto: Re: [Ryu-devel] BGP Next hop on a shared segment
Hi Gabriele,
Thank you for your suggestion!
Your suggestion is it is useful to optimize the NEXT_HOP attribute if routers
share the same segment, right?
You mean Ryu should update the NEXT_HOP attribute?
Thanks,
Iwase
On 2017年12月20日 23:57, Gabriele Lospoto wrote:
> Dear Ryu Team,
> I'm implementing a BGP scenario involving 3 Ryu controllers (each of
> them is running the Ryu BGP application) on a shared LAN (setting is
> enclosed to this email).
>
> This is the control plane BGP table at controller 1 (90.0.0.1):
>
> [
> {
> "paths":
> [
> {
> "origin": "i",
> "aspath": [2],
> "prefix": "25.0.0.0/8",
> "bpr": "AS Path",
> "localpref": "",
> "nexthop": "90.0.0.2",
> "metric": "",
> "labels": null,
> "best": true
> },
> {
> "origin": "i",
> "aspath": [3, 2],
> "prefix": "25.0.0.0/8",
> "bpr": "",
> "localpref": "",
> "nexthop": "90.0.0.3",
> "metric": "",
> "labels": null,
> "best": false
> }
> ],
> "prefix": "25.0.0.0/8"
> },
> {
> "paths":
> [
> {
> "origin": "i",
> "aspath": [3],
> "prefix": "35.0.0.0/8",
> "bpr": "AS Path",
> "localpref": "",
> "nexthop": "90.0.0.3",
> "metric": "",
> "labels": null,
> "best": true
> },
> {
> "origin": "i",
> "aspath": [2, 3],
> "prefix": "35.0.0.0/8",
> "bpr": "",
> "localpref": "",
> "nexthop": "90.0.0.2",
> "metric": "",
> "labels": null,
> "best": false
> }
> ],
> "prefix": "35.0.0.0/8"
> },
> {
> "paths":
> [
> {
> "origin": "i",
> "aspath": [],
> "prefix": "15.0.0.0/8",
> "bpr": "Only Path",
> "localpref": "",
> "nexthop": "0.0.0.0",
> "metric": "",
> "labels": null,
> "best": true
> }
> ],
> "prefix": "15.0.0.0/8"
> }
> ]
>
> As you can see, for prefix 25.0.0.0/8 and 35.0.0.0/8 there are two
> different alternatives, but I was expecting that the next hop stays
> unchanged due to the "shared segment (or media)" optimization. Even RFC
> 4271 opens to this possibility in the section 5.1.3 at point 2) when
> they say:
>
> "Otherwise, if the route being announced was learned from an external
> peer the speaker can use an IP address of any adjacent router (known
> from the received NEXT_HOP attribute) that the speaker itself uses for
> local route calculation in the NEXT_HOP attribute, provided that peer X
> shares a common subnet with this address. This is a second form of
> "third party" NEXT_HOP attribute".
>
> I know, this is just an optimization, but it is implemented in other BGP
> implementation (e.g. Quagga), as you can see in the following (control
> plane BGP table on BGP speaker 90.0.0.1 in a scenario with Quagga BGP
> speaker in place of a Ryu BGP speaker):
>
> r1# show ip bgp
> BGP table version is 0, local router ID is 90.0.0.1
> Status codes: s suppressed, d damped, h history, * valid, > best, =
> multipath,
> i internal, r RIB-failure, S Stale, R Removed
> Origin codes: i - IGP, e - EGP, ? - incomplete
>
> Network Next Hop Metric LocPrf Weight Path
> *> 15.0.0.0 0.0.0.0 0 32768 i
> * 25.0.0.0 90.0.0.2 0 3 2 i
> *> 90.0.0.2 0 0 2 i
> * 35.0.0.0 90.0.0.3 0 2 3 i
> *> 90.0.0.3 0 0 3 i
>
> Am I wronging something?
> Thanks in advance.
> Gabriele
>
>
>
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