'prefer older' does not work?
Hello! All of our BGP peers have 'prefer older' option enabled. But I noticed that best route is not the oldest one: bird> show route for 91.226.190.1 all 91.226.190.0/24 via 193.25.181.44 on bge0 [ITSTARCOM 2019-05-10 11:05:56] * (100) [AS50981i] Type: BGP unicast univ BGP.origin: IGP BGP.as_path: 48422 50981 BGP.next_hop: 193.25.181.44 BGP.local_pref: 100 BGP.community: (65005,10804) (31210,31210) BGP.ext_community: (rt, 31210, 31210) via 193.25.180.141 on bge0 [SATELLITE 2019-05-09 15:16:08] (100) [AS50981i] Type: BGP unicast univ BGP.origin: IGP BGP.as_path: 44416 50981 BGP.next_hop: 193.25.180.141 BGP.local_pref: 100 BGP.community: (44416,2) (65005,10804) (31210,31210) BGP.ext_community: (rt, 31210, 31210) What am I missing? Thanks! -- Alexander Shikov Technical Staff, Digital Telecom IX Tel.: +380 44 201 14 07 Mob.: +380 50 410 30 57 http://dtel-ix.net/
Hi Alexander, Suggest you confirm with the BGP route selection algorithm bgp_rte_better, the option "prefer older" will work only when all pervious selection options are the same. Best Regards, Arvin Gan -----Original Message----- From: Bird-users <bird-users-bounces@network.cz> On Behalf Of Alexander Shikov Sent: Monday, May 13, 2019 5:49 PM To: bird-users@network.cz Subject: 'prefer older' does not work? Hello! All of our BGP peers have 'prefer older' option enabled. But I noticed that best route is not the oldest one: bird> show route for 91.226.190.1 all 91.226.190.0/24 via 193.25.181.44 on bge0 [ITSTARCOM 2019-05-10 11:05:56] * (100) [AS50981i] Type: BGP unicast univ BGP.origin: IGP BGP.as_path: 48422 50981 BGP.next_hop: 193.25.181.44 BGP.local_pref: 100 BGP.community: (65005,10804) (31210,31210) BGP.ext_community: (rt, 31210, 31210) via 193.25.180.141 on bge0 [SATELLITE 2019-05-09 15:16:08] (100) [AS50981i] Type: BGP unicast univ BGP.origin: IGP BGP.as_path: 44416 50981 BGP.next_hop: 193.25.180.141 BGP.local_pref: 100 BGP.community: (44416,2) (65005,10804) (31210,31210) BGP.ext_community: (rt, 31210, 31210) What am I missing? Thanks! -- Alexander Shikov Technical Staff, Digital Telecom IX Tel.: +380 44 201 14 07 Mob.: +380 50 410 30 57 http://dtel-ix.net/
On Mon, May 13, 2019 at 12:49:06PM +0300, Alexander Shikov wrote:
Hello!
All of our BGP peers have 'prefer older' option enabled. But I noticed that best route is not the oldest one:
Hi The option 'prefer older' is a bit misnomer, it does not mean the one with the oldest timestamp, but it means 'prefer current best route'. So if route A was selected first, then route B was updated, and then route A was updated again (so it has more recent timestamp), then route A is still selected. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."
On Mon, May 13, 2019 at 02:19:27PM +0200, Ondrej Zajicek wrote:
On Mon, May 13, 2019 at 12:49:06PM +0300, Alexander Shikov wrote:
Hello!
All of our BGP peers have 'prefer older' option enabled. But I noticed that best route is not the oldest one:
Hi
The option 'prefer older' is a bit misnomer, it does not mean the one with the oldest timestamp, but it means 'prefer current best route'.
So if route A was selected first, then route B was updated, and then route A was updated again (so it has more recent timestamp), then route A is still selected.
Thank you, Ondrej. -- Alexander Shikov Technical Staff, Digital Telecom IX Tel.: +380 44 201 14 07 Mob.: +380 50 410 30 57 http://dtel-ix.net/
participants (3)
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Alexander Shikov -
Arvin Gan -
Ondrej Zajicek