Hello Bogdan,

According  to https://www.rfc-editor.org/rfc/rfc4271.html,

"the AGGREGATOR is an attribute of length 6", not 8.

According to https://www.rfc-editor.org/rfc/rfc6793.html,

"the AS4_AGGREGATOR attribute in an UPDATE message SHALL be considered 
malformed if the attribute length is not 8".

I think it looks like a bug in the Mikrotik BGP code that tries to encode AS4 
in an AS attribute.

BR
Jörg


On 29 Jun 2023, at 13:44, Bogdan-Stefan Rotariu wrote:

> Hi there,
>
> We have some CER2024 in our network, and we are starting to encounter issues 
> when receiving prefixes from Mikrotik CCR2216 that is running with ROSv7. Has 
> anyone any ideea except replacing the CER’s?
>
> The peer is has AS4 capability negociated:
>
>    Neighbor AS4 Capability Negotiation:
>      Peer Negotiated AS4  capability
>      Peer configured for AS4  capability
>
> We are running version 6.3.0.fT183:
>
> IronWare : Version 6.3.0fT183 Copyright (c) 2017-2019 Extreme Networks, Inc.
> Compiled on Jul 14 2022 at 21:38:40 labeled as ce06300f
> (18589108 bytes) from Primary
>
> last-packet-with-error decode shows :
>
> Received Message Length: 94
> BGP Message:
>  0xffffffff  0xffffffff  0xffffffff  0xffffffff  0x005e0200
>  0x00004340  0x01010050  0x02001602  0x05000022  0x04000015
>  0xe60000ad  0x820000ad  0x820000ad  0x82400304  0x0a0b010f
>  0x40050400  0x00006440  0x0600d008  0x00042204  0x0064d007
>  0x00080000  0xad825509  0x1f8617c3  0xd204
>
> BGP Header
>  Marker:   0xffffffff  0xffffffff  0xffffffff  0xffffffff
>  Message Length: (0x005e) 94
>  Message Type: (0x02) UPDATE
>
> UPDATE Message
> Unfeasible route length: (0x0000) 0
> Update path attributes
> Total Path Attribute length: (0x0043) 67
>  Flags : (0x40) Well Known, Transitive, Complete
>  Type  : (0x01) Origin
>  Length: (0x01) 1
>  Origin: (0x00) IGP
>
>  Flags : (0x50) Well Known, Transitive, Complete, Extended length
>  Type  : (0x02) AS Path
>  Length: (0x0016) 22
>   Segment Type  : (0x02) AS Sequence
>   Segment Length: (0x05) 5
>   AS Numbers    : (0x0000) 0, (0x2204) 8708, (0x0000) 0, (0x15e6) 5606, 
> (0x0000) 0,
>   Segment Type  : (0xad) Unknown(173)
>   Segment Length: (0x82) 130
>   AS Numbers    : (0x0000) 0, (0xad82) 44418, (0x0000) 0, (0xad82) 44418,
>
>  Flags : (0x40) Well Known, Transitive, Complete
>  Type  : (0x03) Next Hop
>  Length: (0x04) 4
>  Next Hop IP address: (0x0a0b010f) 10.11.1.15
>
>  Flags : (0x40) Well Known, Transitive, Complete
>  Type  : (0x05) Local Preference
>  Length: (0x04) 4
>  Local Preference: (0x00000064) 100
>
>  Flags : (0x40) Well Known, Transitive, Complete
>  Type  : (0x06) Atomic Aggregate
>  Length: (0x00) 0
>
>  Flags : (0xd0) Optional, Transitive, Complete, Extended length
>  Type  : (0x08) Community
>  Length: (0x0004) 4
>  Community List: (0x22040064) 8708:100
>
>  Flags : (0xd0) Optional, Transitive, Complete, Extended length
>  Type  : (0x07) Aggregator
>  Length: (0x0008) 8
> Error: Invalid AGGREGATOR attribute length 8
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