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</head><body text="#485663"><span>Brian Longwe via ixpmanager wrote on
22/07/2026 16:07:</span><br>
<blockquote type="cite"
cite="mid:CAGgOPOaTmBgvinuJB7yGdX4Z8SxGZWmPXc7re=HvSbtDDrszJQ@mail.gmail.com">
<div dir="ltr">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.</div>
</blockquote>
<br>
Hi Brian,<br>
<br>
"AS23456" is the pseudo ASN used for negotiating a BGP session with a
32-bit AS number, so this would be expected in a tcpdump packet capture
for AS139057.<br>
<br>
You received a "Malformed AS_PATH" error from the remote side. This is
usually seen on Cisco and similar style BGP stacks which expect the AS
Path to include the peer AS as the first ASN in the AS path. This
doesn't happen at a route server, so all Cisco style customers of yours
need to include "no bgp enforce-first-as" in the "router bgp" stanza of
their configuration. Once this is configured, the BGP session should
work fine.<br>
<br>
Nick<br>
<br>
<br>
<blockquote type="cite"
cite="mid:CAGgOPOaTmBgvinuJB7yGdX4Z8SxGZWmPXc7re=HvSbtDDrszJQ@mail.gmail.com">
<div dir="ltr">
<div class="gmail_quote gmail_quote_container">
<div dir="ltr"><div>Any idea how we can fix this? Is there a
skin/neighbor profile that we can configure for them?</div><div><br></div><div>Here
is output from birdc show protocol:</div><div><br></div><div>root@rs1:/home/devops#
/usr/sbin/birdc -s /var/run/bird/bird-rs1-lan1-ipv4.ctl<br>BIRD 2.19.1
ready.<br>bird> show protocols all pb_0025_as139057<br>Name
Proto Table State Since Info<br>pb_0025_as139057 BGP
--- start 2026-07-22 14:45:32 Idle Received:
Malformed AS_PATH<br> Description: AS139057 - CDN EdgeNext<br> BGP
state: Idle<br> Neighbor address: 196.x.y.z<br> Neighbor
AS: 139057<br> Local AS: 37800<br> Error wait:
35.054/60<br> Last error: Received: Malformed AS_PATH<br>
Channel ipv4<br> State: DOWN<br> Table:
t_0025_as139057<br> Preference: 100<br> Input filter:
f_import_as139057<br> Output filter: f_export_as139057<br> Import
limit: 1000<br> Action: restart</div><div><br></div><div>And
here is output from tcpdump packet capture:</div><div>11:38:15.176666
ens18 In IP (tos 0xc0, ttl 1, id 36934, offset 0, flags [none], proto
TCP (6), length 123)<br> 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<br> Open
Message (1), length: 71<br> Version 4, my AS 23456, Holdtime 180s, ID
172.16.0.1<br> Optional parameters, length: 42<br> Option
Capabilities Advertisement (2), length: 6<br> Multiprotocol
Extensions (1), length: 4<br> AFI IPv4 (1), SAFI Unicast (1)<br>
0x0000: 0001 0001<br> Option Capabilities Advertisement (2),
length: 2<br> Route Refresh (Cisco) (128), length: 0<br>
Option Capabilities Advertisement (2), length: 2<br> Route
Refresh (2), length: 0<br> Option Capabilities Advertisement (2),
length: 16<br> Graceful Restart (64), length: 14<br> Restart
Flags: [none], Restart Time 120s<br> AFI IPv4 (1), SAFI Unicast (1),
Forwarding state preserved: yes<br> AFI IPv6 (2), SAFI Unicast (1),
Forwarding state preserved: yes<br> AFI VPLS (25), SAFI EVPN (70),
Forwarding state preserved: yes<br> 0x0000: 0078 0001 0180 0002 0180
0019 4680<br> Option Capabilities Advertisement (2), length: 6<br>
32-Bit AS Number (65), length: 4<br> 4 Byte AS 139057<br> 0x0000:
0002 1f31<br> 0x0000: 45c0 007b 9046 0000 0106 abce c43c 7a2c
E..{.F.......<z,<br> 0x0010: c43c 7a03 c1ad 00b3 da49 51e5 b19f
25d5 .<z......IQ...%.<br> 0x0020: 8018 16d0 56b2 0000 0101 080a
027c 7e88 ....V........|~.<br> 0x0030: e4e1 ac2f ffff ffff ffff ffff
ffff ffff .../............<br> 0x0040: ffff ffff 0047 0104 5ba0 00b4
ac10 0001 .....G..[.......<br> 0x0050: 2a02 0601 0400 0100 0102 0280
0002 0202 *...............<br> 0x0060: 0002 1040 0e00 7800 0101 8000
0201 8000 ...@..x.........<br> 0x0070: 1946 8002 0641 0400 021f 31
.F...A....1<br>11:38:15.176686 ens18 Out IP (tos 0xc0, ttl 64,
id 0, offset 0, flags [DF], proto TCP (6), length 40)<br>
rs1-lan1-ipv4.bgp > 196.60.122.44.49581: Flags [R], cksum 0x9962
(correct), seq 2979997141, win 0, length 0<br> 0x0000: 45c0 0028 0000
4000 4006 bd67 c43c 7a03 E..(..@.@..g.<z.<br> 0x0010: c43c 7a2c
00b3 c1ad b19f 25d5 0000 0000 .<z,......%.....<br> 0x0020: 5004
0000 9962 0000 P....b..<br>11:38:26.177549 ens18 In
IP (tos 0xc0, ttl 1, id 37226, offset 0, flags [none], proto TCP (6),
length 60)<br> 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<br> 0x0000:
45c0 003c 916a 0000 0106 aae9 c43c 7a2c E..<.j.......<z,<br>
0x0010: c43c 7a03 ab24 00b3 7c53 a00e 0000 0000 .<z..$..|S......<br>
0x0020: a002 16d0 6704 0000 0204 05b4 0402 080a ....g...........<br>
0x0030: 027c 82d4 0000 0000 0103 0300 .|..........<br>11:38:26.177593
ens18 Out IP (tos 0xc0, ttl 255, id 0, offset 0, flags [DF], proto TCP
(6), length 60)<br> rs1-lan1-ipv4.bgp > 196.60.122.44.43812: Flags
[S.], cksum 0x7cd7 (incorrect -> 0x8971), seq 316352219, ack
2085855247, win 65160, options [mss 1460,sackOK,TS val 3840005929 ecr
41714388,nop,wscale 7], length 0<br> 0x0000: 45c0 003c 0000 4000 ff06
fe52 c43c 7a03 E..<..@....R.<z.<br> 0x0010: c43c 7a2c 00b3 ab24
12db 26db 7c53 a00f .<z,...$..&.|S..<br> 0x0020: a012 fe88 7cd7
0000 0204 05b4 0402 080a ....|...........<br> 0x0030: e4e1 d729 027c
82d4 0103 0307 ...).|......<br>11:38:26.179093 ens18 In IP
(tos 0xc0, ttl 1, id 37227, offset 0, flags [none], proto TCP (6),
length 52)<br> 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<br> 0x0000: 45c0 0034 916b 0000
0106 aaf0 c43c 7a2c E..4.k.......<z,<br> 0x0010: c43c 7a03 ab24
00b3 7c53 a00f 12db 26dc .<z..$..|S....&.<br> 0x0020: 8010 16d0
9ff6 0000 0101 080a 027c 82d4 .............|..<br> 0x0030: e4e1 d729
...)<br>11:38:26.179093 ens18 In IP (tos
0xc0, ttl 1, id 37228, offset 0, flags [none], proto TCP (6), length 52)<br>
196.60.122.44.43812 > rs1-lan1-ipv4.bgp: Flags [.], cksum 0x9ff6
(correct), seq 1, ack 1, win 5840, options [nop,nop,TS val 41714388 ecr
3840005929], length 0<br> 0x0000: 45c0 0034 916c 0000 0106 aaef c43c
7a2c E..4.l.......<z,<br> 0x0010: c43c 7a03 ab24 00b3 7c53 a00f
12db 26dc .<z..$..|S....&.<br> 0x0020: 8010 16d0 9ff6 0000 0101
080a 027c 82d4 .............|..<br> 0x0030: e4e1 d729
...)<br>11:38:26.179093 ens18 In IP (tos 0xc0, ttl 1,
id 37229, offset 0, flags [none], proto TCP (6), length 123)<br>
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<br> Open Message (1), length: 71<br>
Version 4, my AS 23456, Holdtime 180s, ID 172.16.0.1<br> Optional
parameters, length: 42<br> Option Capabilities Advertisement (2),
length: 6<br> Multiprotocol Extensions (1), length: 4<br> AFI
IPv4 (1), SAFI Unicast (1)<br> 0x0000: 0001 0001<br> Option
Capabilities Advertisement (2), length: 2<br> Route Refresh
(Cisco) (128), length: 0<br> Option Capabilities Advertisement (2),
length: 2<br> Route Refresh (2), length: 0<br> Option
Capabilities Advertisement (2), length: 16<br> Graceful Restart
(64), length: 14<br> Restart Flags: [none], Restart Time 120s<br>
AFI IPv4 (1), SAFI Unicast (1), Forwarding state preserved: yes<br>
AFI IPv6 (2), SAFI Unicast (1), Forwarding state preserved: yes<br>
AFI VPLS (25), SAFI EVPN (70), Forwarding state preserved: yes<br>
0x0000: 0078 0001 0180 0002 0180 0019 4680<br> Option Capabilities
Advertisement (2), length: 6<br> 32-Bit AS Number (65), length: 4<br>
4 Byte AS 139057<br> 0x0000: 0002 1f31<br> 0x0000: 45c0 007b 916d
0000 0106 aaa7 c43c 7a2c E..{.m.......<z,<br> 0x0010: c43c 7a03
ab24 00b3 7c53 a00f 12db 26dc .<z..$..|S....&.<br> 0x0020: 8018
16d0 eb7e 0000 0101 080a 027c 82d4 .....~.......|..<br> 0x0030: e4e1
d729 ffff ffff ffff ffff ffff ffff ...)............<br> 0x0040: ffff
ffff 0047 0104 5ba0 00b4 ac10 0001 .....G..[.......<br> 0x0050: 2a02
0601 0400 0100 0102 0280 0002 0202 *...............<br> 0x0060: 0002
1040 0e00 7800 0101 8000 0201 8000 ...@..x.........<br> 0x0070: 1946
8002 0641 0400 021f 31 .F...A....1<br><br><br></div><div><div
dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div
dir="ltr"><div>--</div><div>Brian Munyao Longwe</div><div>IXP
Coordinator | Cell: +265999708883</div><div><a href="https://lionex.org"
target="_blank" moz-do-not-send="true"><img alt="https://lionex.org"
src="https://ci3.googleusercontent.com/mail-sig/AIorK4xJpwdHsBCQuenqp2oA-Ybvd4brYWH0KCcnblD5Wk1Jiedkvmlbd9hujA3vKzAcGpVQY8Uz2rEo1J7T"
moz-do-not-send="true"></a></div></div></div></div></div>
</div>
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</blockquote>
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