[ixpmanager] Fwd: Malformed AS_PATH BGP Error Message from CDN Peer
Brian Longwe
brian at lionex.org
Wed Jul 22 16:07:04 IST 2026
Hi,
Strange problem here. We have just turned up a new CDN at our IXP -
EdgeNext. Our Route Server is refusing to peer with them, citing the error
"Malformed AS_PATH". Tcpdump shows them having a "my AS" of 123456 - which
it seems Bird is misunderstanding.
Any idea how we can fix this? Is there a skin/neighbor profile that we can
configure for them?
Here is output from birdc show protocol:
root at rs1:/home/devops# /usr/sbin/birdc -s
/var/run/bird/bird-rs1-lan1-ipv4.ctl
BIRD 2.19.1 ready.
bird> show protocols all pb_0025_as139057
Name Proto Table State Since Info
pb_0025_as139057 BGP --- start 2026-07-22 14:45:32 Idle
Received: Malformed AS_PATH
Description: AS139057 - CDN EdgeNext
BGP state: Idle
Neighbor address: 196.x.y.z
Neighbor AS: 139057
Local AS: 37800
Error wait: 35.054/60
Last error: Received: Malformed AS_PATH
Channel ipv4
State: DOWN
Table: t_0025_as139057
Preference: 100
Input filter: f_import_as139057
Output filter: f_export_as139057
Import limit: 1000
Action: restart
And here is output from tcpdump packet capture:
11:38:15.176666 ens18 In IP (tos 0xc0, ttl 1, id 36934, offset 0, flags
[none], proto TCP (6), length 123)
196.60.122.44.49581 > rs1-lan1-ipv4.bgp: Flags [P.], cksum 0x56b2
(correct), seq 1:72, ack 1, win 5840, options [nop,nop,TS val 41713288 ecr
3839994927], length 71: BGP
Open Message (1), length: 71
Version 4, my AS 23456, Holdtime 180s, ID 172.16.0.1
Optional parameters, length: 42
Option Capabilities Advertisement (2), length: 6
Multiprotocol Extensions (1), length: 4
AFI IPv4 (1), SAFI Unicast (1)
0x0000: 0001 0001
Option Capabilities Advertisement (2), length: 2
Route Refresh (Cisco) (128), length: 0
Option Capabilities Advertisement (2), length: 2
Route Refresh (2), length: 0
Option Capabilities Advertisement (2), length: 16
Graceful Restart (64), length: 14
Restart Flags: [none], Restart Time 120s
AFI IPv4 (1), SAFI Unicast (1), Forwarding state preserved: yes
AFI IPv6 (2), SAFI Unicast (1), Forwarding state preserved: yes
AFI VPLS (25), SAFI EVPN (70), Forwarding state preserved: yes
0x0000: 0078 0001 0180 0002 0180 0019 4680
Option Capabilities Advertisement (2), length: 6
32-Bit AS Number (65), length: 4
4 Byte AS 139057
0x0000: 0002 1f31
0x0000: 45c0 007b 9046 0000 0106 abce c43c 7a2c E..{.F.......<z,
0x0010: c43c 7a03 c1ad 00b3 da49 51e5 b19f 25d5 .<z......IQ...%.
0x0020: 8018 16d0 56b2 0000 0101 080a 027c 7e88 ....V........|~.
0x0030: e4e1 ac2f ffff ffff ffff ffff ffff ffff .../............
0x0040: ffff ffff 0047 0104 5ba0 00b4 ac10 0001 .....G..[.......
0x0050: 2a02 0601 0400 0100 0102 0280 0002 0202 *...............
0x0060: 0002 1040 0e00 7800 0101 8000 0201 8000 ... at ..x.........
0x0070: 1946 8002 0641 0400 021f 31 .F...A....1
11:38:15.176686 ens18 Out IP (tos 0xc0, ttl 64, id 0, offset 0, flags [DF],
proto TCP (6), length 40)
rs1-lan1-ipv4.bgp > 196.60.122.44.49581: Flags [R], cksum 0x9962
(correct), seq 2979997141, win 0, length 0
0x0000: 45c0 0028 0000 4000 4006 bd67 c43c 7a03 E..(.. at .@..g.<z.
0x0010: c43c 7a2c 00b3 c1ad b19f 25d5 0000 0000 .<z,......%.....
0x0020: 5004 0000 9962 0000 P....b..
11:38:26.177549 ens18 In IP (tos 0xc0, ttl 1, id 37226, offset 0, flags
[none], proto TCP (6), length 60)
196.60.122.44.43812 > rs1-lan1-ipv4.bgp: Flags [S], cksum 0x6704
(correct), seq 2085855246, win 5840, options [mss 1460,sackOK,TS val
41714388 ecr 0,nop,wscale 0], length 0
0x0000: 45c0 003c 916a 0000 0106 aae9 c43c 7a2c E..<.j.......<z,
0x0010: c43c 7a03 ab24 00b3 7c53 a00e 0000 0000 .<z..$..|S......
0x0020: a002 16d0 6704 0000 0204 05b4 0402 080a ....g...........
0x0030: 027c 82d4 0000 0000 0103 0300 .|..........
11:38:26.177593 ens18 Out IP (tos 0xc0, ttl 255, id 0, offset 0, flags
[DF], proto TCP (6), length 60)
rs1-lan1-ipv4.bgp > 196.60.122.44.43812: Flags [S.], cksum 0x7cd7
(incorrect -> 0x8971), seq 316352219, ack 2085855247, win 65160, options
[mss 1460,sackOK,TS val 3840005929 ecr 41714388,nop,wscale 7], length 0
0x0000: 45c0 003c 0000 4000 ff06 fe52 c43c 7a03 E..<.. at ....R.<z.
0x0010: c43c 7a2c 00b3 ab24 12db 26db 7c53 a00f .<z,...$..&.|S..
0x0020: a012 fe88 7cd7 0000 0204 05b4 0402 080a ....|...........
0x0030: e4e1 d729 027c 82d4 0103 0307 ...).|......
11:38:26.179093 ens18 In IP (tos 0xc0, ttl 1, id 37227, offset 0, flags
[none], proto TCP (6), length 52)
196.60.122.44.43812 > rs1-lan1-ipv4.bgp: Flags [.], cksum 0x9ff6
(correct), seq 1, ack 1, win 5840, options [nop,nop,TS val 41714388 ecr
3840005929], length 0
0x0000: 45c0 0034 916b 0000 0106 aaf0 c43c 7a2c E..4.k.......<z,
0x0010: c43c 7a03 ab24 00b3 7c53 a00f 12db 26dc .<z..$..|S....&.
0x0020: 8010 16d0 9ff6 0000 0101 080a 027c 82d4 .............|..
0x0030: e4e1 d729 ...)
11:38:26.179093 ens18 In IP (tos 0xc0, ttl 1, id 37228, offset 0, flags
[none], proto TCP (6), length 52)
196.60.122.44.43812 > rs1-lan1-ipv4.bgp: Flags [.], cksum 0x9ff6
(correct), seq 1, ack 1, win 5840, options [nop,nop,TS val 41714388 ecr
3840005929], length 0
0x0000: 45c0 0034 916c 0000 0106 aaef c43c 7a2c E..4.l.......<z,
0x0010: c43c 7a03 ab24 00b3 7c53 a00f 12db 26dc .<z..$..|S....&.
0x0020: 8010 16d0 9ff6 0000 0101 080a 027c 82d4 .............|..
0x0030: e4e1 d729 ...)
11:38:26.179093 ens18 In IP (tos 0xc0, ttl 1, id 37229, offset 0, flags
[none], proto TCP (6), length 123)
196.60.122.44.43812 > rs1-lan1-ipv4.bgp: Flags [P.], cksum 0xeb7e
(correct), seq 1:72, ack 1, win 5840, options [nop,nop,TS val 41714388 ecr
3840005929], length 71: BGP
Open Message (1), length: 71
Version 4, my AS 23456, Holdtime 180s, ID 172.16.0.1
Optional parameters, length: 42
Option Capabilities Advertisement (2), length: 6
Multiprotocol Extensions (1), length: 4
AFI IPv4 (1), SAFI Unicast (1)
0x0000: 0001 0001
Option Capabilities Advertisement (2), length: 2
Route Refresh (Cisco) (128), length: 0
Option Capabilities Advertisement (2), length: 2
Route Refresh (2), length: 0
Option Capabilities Advertisement (2), length: 16
Graceful Restart (64), length: 14
Restart Flags: [none], Restart Time 120s
AFI IPv4 (1), SAFI Unicast (1), Forwarding state preserved: yes
AFI IPv6 (2), SAFI Unicast (1), Forwarding state preserved: yes
AFI VPLS (25), SAFI EVPN (70), Forwarding state preserved: yes
0x0000: 0078 0001 0180 0002 0180 0019 4680
Option Capabilities Advertisement (2), length: 6
32-Bit AS Number (65), length: 4
4 Byte AS 139057
0x0000: 0002 1f31
0x0000: 45c0 007b 916d 0000 0106 aaa7 c43c 7a2c E..{.m.......<z,
0x0010: c43c 7a03 ab24 00b3 7c53 a00f 12db 26dc .<z..$..|S....&.
0x0020: 8018 16d0 eb7e 0000 0101 080a 027c 82d4 .....~.......|..
0x0030: e4e1 d729 ffff ffff ffff ffff ffff ffff ...)............
0x0040: ffff ffff 0047 0104 5ba0 00b4 ac10 0001 .....G..[.......
0x0050: 2a02 0601 0400 0100 0102 0280 0002 0202 *...............
0x0060: 0002 1040 0e00 7800 0101 8000 0201 8000 ... at ..x.........
0x0070: 1946 8002 0641 0400 021f 31 .F...A....1
--
Brian Munyao Longwe
IXP Coordinator | Cell: +265999708883
[image: https://lionex.org] <https://lionex.org>
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