Weird IPv6 problem passing Layer3 traffic

[Matthew Huff]

Trying to bring up a new BGP peering session with a ISP. IPv4 peering is working fine on the same interface. The BGP peering fails early in trying to go active. Using "debug tcp transactions", I see the SYN going out, but no ACK ever returning. I can't telnet to their box on port 179 either (debug packet shows it doing the same, SYN begin sent, but no packets, including ACK). However, I can ping their interface.

The interface config has been stripped, and still doesn't work. I've reset the interface, and even rebooted our router, with no change in behavior.

We have a Cisco 7204VXR with NPE-G2, running 15.2(4)S1. I have an identical router with same version connected to another ISP and a tunnel to HE.net. It's not my first time at the rodeo. We are connected via metro Ethernet to a sub-interface on a JunOS box (model and version unknown). My suspicion is that either they have an ACL that's blocking it, or their BGP process isn't listening on that sub-interface. But they claim that it isn't their problem. I have zero JunOS experience and they seem to be flopping around.

Anyone have any idea what else the problem might be?

>From our side (simplied config to test):


interface FastEthernet2/1
 ip address 162.211.110.2 255.255.255.252
 speed auto
 duplex auto
 ipv6 address 2607:F518:15F::2/126
 ipv6 enable
end

rtr-inet2#show ipv6 cef 2607:F518:15F::1 
2607:F518:15F::1/128
  attached to FastEthernet2/1

rtr-inet2#show ipv6 cef exact-route 2607:F518:15F::2 2607:F518:15F::1
2607:F518:15F::2 -> 2607:F518:15F::1 => IPV6 adj out of FastEthernet2/1, addr 2607:F518:15F::1

rtr-inet2#show ipv6 neighbors            
IPv6 Address                              Age Link-layer Addr State Interface
2607:F518:15F::1                            0 0021.5903.1367  REACH Fa2/1

rtr-inet2#ping  2607:F518:15F::1 
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2607:F518:15F::1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

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Matthew Huff             | 1 Manhattanville Rd
Director of Operations   | Purchase, NY 10577
OTA Management LLC       | Phone: 914-460-4039