Hi everybody, I am very certain somebody has experienced similar issues and solved them; I did not find any pointers - please throw them at me. If this is new or unsolved, please help me forward, I can get more output, naturally. Thank you for your interest already! Elmar. The setup: - Pair of Cisco ASR9K running IOS XR trunked to a Juniper EX. - FreeBSD 12.1-RELEASE-p3 with bird 2.07, on an access port of that switch. - Straightforward OSPF setup on the XR, simple BIRD setup on the BSD. The issue: - BIRD connects nicely on OSPFv2 (for IPv4), all's good. - BIRD stays "alone" on OSPFv3 (for IPv6), the Cisco box stays in state EXSTART/DROTHER The awkwardness: - OSPF for IPv4 works just fine. XR config is identical. - Quagga ospf3d does the job just fine. The XR config: router ospfv3 <instance> router-id <router-1> default-information originate area 0 interface TenGigE0/1/0/23.4 The BIRD config (snippets): === v4 config === protocol ospf v2 { area 0 { interface "lo0" { stub; }; interface "*" { }; }; ipv4 { import filter ospf_v4_in; export filter ospf_v4_out; }; } === v6 config === protocol ospf v3 { area 0 { interface "lo0" { stub; }; interface "*" { }; }; ipv6 { import filter ospf_v6_in; export filter ospf_v6_out; }; } The BIRD outputs: ospf1 OSPF master4 up 2020-05-27 Running ospf2 OSPF master6 up 2020-05-27 Alone Name Proto Table State Since Info ospf2 OSPF master6 up 2020-05-27 Alone Channel ipv6 State: UP Table: master6 Preference: 150 Input filter: ospf_v6_in Output filter: ospf_v6_out Routes: 0 imported, 0 exported, 0 preferred Route change stats: received rejected filtered ignored accepted Import updates: 1 0 1 0 0 Import withdraws: 0 0 --- 1 0 Export updates: 0 0 0 --- 0 Export withdraws: 0 --- --- --- 0 The relevant *ahem* BIRD debug log output (yes, I googled) 2020-05-31 13:08:15.080 <RMT> ospf2: Bad DBDES packet from nbr <router-1> on igb0 - I-bit mismatch (7) The Cisco side of things (debug ipv6 ospf <instance> adj) May 31 13:09:16.278 UTC: ospfv3[1021]: ADJ: Send DBD to <server> on TenGigE0/1/0/23.4 seq 0x8ce5d69 opt R/E/V6 flag I/M/MS len 28 mtu 1500 May 31 13:09:16.278 UTC: ospfv3[1021]: ADJ: Retransmitting DBD to <server> on TenGigE0/1/0/23.4 [1] May 31 13:09:16.278 UTC: ospfv3[1021]: ADJ: Recv DBD fr <server> on TenGigE0/1/0/23.4 seq 0x8ce5d69 opt R/E/V6 flag NONE len 108 mtu 1500 state EXSTART May 31 13:09:16.278 UTC: ospfv3[1021]: ADJ: Build DBD summary list for <server> May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: Built DBD summary list in 0 ms for <server>, 65 entries May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: new: type 2001 lsid 0x0 adv <server> seq 0x800000af age 612 May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: new: type 2009 lsid 0x0 adv <server> seq 0x800000af age 612 May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: new: type 0008 lsid 0x1 adv <server> seq 0x800000af age 612 May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: Send DBD to <server> on TenGigE0/1/0/23.4 seq 0x8ce5d6a opt R/E/V6 flag M/MS len 1228 mtu 1500 May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: Build REQ packet for <server> May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: type 2001 lsid 0x0 adv <server> May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: type 2009 lsid 0x0 adv <server> May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: type 0008 lsid 0x1 adv <server> May 31 13:09:16.279 UTC: ospfv3[1021]: ADJ: Send REQ packet to <server>, length 36 May 31 13:09:16.280 UTC: ospfv3[1021]: ADJ: Recv DBD fr <server> on TenGigE0/1/0/23.4 seq 0x8ce5d6a opt R/E/V6 flag NONE len 28 mtu 1500 state EXCHANGE May 31 13:09:16.280 UTC: ospfv3[1021]: ADJ: Send DBD to <server> on TenGigE0/1/0/23.4 seq 0x8ce5d6b opt R/E/V6 flag I/M/MS len 28 mtu 1500 May 31 13:09:16.281 UTC: ospfv3[1021]: ADJ: Recv DBD fr <server> on TenGigE0/1/0/23.4 seq 0x8ce5d6b opt R/E/V6 flag I/M/MS len 28 mtu 1500 state EXSTART