Hi
On 8/8/25 3:14 PM, Matthew Smith via lists.fd.io wrote:
You could try adding del-dynamic-on-link-down to the linux-cp
section of your startup.conf and see if that helps.
I've tried this parameter, but it didn't make a difference when bringing
the iBGP session down.
Now that I'm inspecting this more closely, I've found some strange
behavior where the VPP routes don't match the ones installed by Bird.
In this case, I've started bird with the uplink BGP session enabled, and
afterwards started the iBGP session. I've noticed the VPP FIB has ~24k
routes pointing to my other router, that is, learned via the iBGP
session. This is weird because routes via the other router should only
be used in case the BGP session with the uplink peer goes down, as they
by definition have one extra hop, and are therefore "worse".
I've checked that bird is indeed selecting the uplink route as the
preferred one. One example:
# birdc show route for 45.181.63.0/24
BIRD 2.16.1 ready.
Table master4:
45.181.63.0/24 unicast [uplink_ipv4 17:44:31.966] * (100) [AS269170i]
via x.y.z.w on uplink1
unicast [ibgp_ipv4 17:44:31.609] (100) [AS269170i]
via a.b.c.d on external
The kernel route is in agreement:
# ip route show 45.181.63.0/24
45.181.63.0/24 via x.y.z.w dev uplink1 proto bird metric 32
But the route in VPP is through my other router (a.b.c.d):
# vppctl show ip fib 45.181.63.0/24
ipv4-VRF:0, fib_index:0, flow hash:[src dst sport dport proto flowlabel
] epoch:0 flags:none locks:[adjacency:1, default-route:1, lcp-rt:1, ]
45.181.63.0/24 fib:0 index:18181 locks:2
lcp-rt-dynamic refs:1 src-flags:added,contributing,active,
path-list:[77] locks:49272 flags:shared,popular, uPRF-list:69 len:1
itfs:[7, ]
path:[103] pl-index:77 ip4 weight=1 pref=32 attached-nexthop:
oper-flags:resolved,
a.b.c.d BondEthernet0
[@0]: ipv4 via a.b.c.d BondEthernet0: mtu:1500 next:8 flags:[]
12b9c288223f3cfdfe9ec4e40800
forwarding: unicast-ip4-chain
[@0]: dpo-load-balance: [proto:ip4 index:18182 buckets:1 uRPF:69
to:[0:0]]
[0] [@5]: ipv4 via a.b.c.d BondEthernet0: mtu:1500 next:8 flags:[]
12b9c288223f3cfdfe9ec4e40800
ipv4-VRF:180, fib_index:1, flow hash:[src dst sport dport proto
flowlabel ] epoch:0 flags:none locks:[lcp-rt:1, ]
0.0.0.0/0 fib:1 index:49 locks:2
default-route refs:1 entry-flags:drop,
src-flags:added,contributing,active,
path-list:[66] locks:2 flags:drop, uPRF-list:62 len:0 itfs:[]
path:[92] pl-index:66 ip4 weight=1 pref=0 special: cfg-flags:drop,
[@0]: dpo-drop ip4
forwarding: unicast-ip4-chain
[@0]: dpo-load-balance: [proto:ip4 index:50 buckets:1 uRPF:62 to:[0:0]]
[0] [@0]: dpo-drop ip4
I don't really know how to explain that.
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