eBGP not establishing

RouterOS Forwarding Protocols
1

I have two new directly connected CRS354-48G-4S+2Q+ running RouterOS 7.11.3. They are directly connected on ether1. Ping works both ways, but eBGP won’t establish. When running a packet capture, I can see a SYN from sw1, SYN-ACK from sw2, and then packets are retransmitted. I’ve replicated this setup on a different pair of brand new CRS354, and the same thing is happening.

sw1:
/ip address
add address=10.255.255.2/30 interface=ether1 network=10.255.255.0
/routing bgp connection
add as=65001 disabled=no local.address=10.255.255.2 .role=ebgp name=test remote.address=10.255.255.3 .as=65000 routing-table=main


sw2:
/ip address
add address=10.255.255.3/30 interface=ether1 network=10.255.255.0
/routing bgp connection
add as=65000 disabled=no local.address=10.255.255.3 .role=ebgp name=test remote.address=10.255.255.2 .as=65001 routing-table=main

Any ideas as to what can be happening?

2

You must not assign subnets broadcast address to host.

3

Thank you. Would be helpful to put that information in the manual as I didn’t find it anywhere. Apologies in advance if it already exists there.

4

that is networking basics

5

Already exists here: https://help.mikrotik.com/docs/spaces/ROS/pages/328247/IP+Addressing#IPAddressing-AddingIPAddress

6

I wonder why Cisco and Arista can support them

7

RFC 3021 compliance dictates that assigning the broadcast address of a /31 is not problematic. I don’t see anything in the official Mikrotik documentation describing support for RFC 3021, but I have seen a few forum posts mentioning that >=7.13 supports it, so while it is indeed networking basics to not allow assigning the broadcast address of a non /31 subnet, it would be useful for Mikrotik to document which RouterOS versions support RFC 3021. I tested this on 7.11 and the symptoms are the same as OP’s:

Router 1

/ip address
add address=10.255.255.6/31 interface=ether2 network=10.255.255.6

/routing bgp connection
add as=65006 local.role=ebgp name=test remote.address=10.255.255.7 .as=65004

Router 2

/ip address
add address=10.255.255.7/31 interface=ether4 network=10.255.255.6

/routing bgp connection
add as=65004 local.role=ebgp name=test remote.address=10.255.255.6 .as=65006
8

RFC3021 is for point-to-point links. Back in the day, on Cisco one had to explicitly configure the interface with the keyword “point-to-point”.

Not by a MT device right now but will definitely try tomorrow.

9

OP clearly hows that broadcast address of /30 is used, it has nothing to do with /31

10

I’ve upgraded firmware to RouterOS 7.16.2 and attempting to use a /31 on a point to point link without success. Is there support for RFC 3021 on this platform or do I need to use a /30 and a non-broadcast address?

11

/31 is just added in 7.18b2, earlier version do not understand that.