TCP connect doesn't establish through IPSEC tunnel

MaximBudyonny · ‎06-13-2007

I have IPSEC tunnel mode between router R1 and router R2.

Crypto session is UP. (sh crypto se)

But when I want to establish TCP connection (e.g. telnet 172.23.250.13 5023) from router R1 inside network to router R2 inside network session doesn't create.

R2

====

R2#sh crypto session detail | s 172.23.250.13

IPSEC FLOW: permit 6 host 172.23.250.13 port 5023 0.0.0.0/0.0.0.0

Active SAs: 2, origin: crypto map

Inbound: #pkts dec'ed 2 drop 0 life (KB/Sec) 4413690/286

Outbound: #pkts enc'ed 3 drop 0 life (KB/Sec) 4413690/286

R1

====

R1#sh crypto session detail | s 172.23.250.13

IPSEC FLOW: permit 6 0.0.0.0/0.0.0.0 host 172.23.250.13 port 5023

Active SAs: 2, origin: crypto map

Inbound: #pkts dec'ed 0 drop 0 life (KB/Sec) 4509190/281

Outbound: #pkts enc'ed 2 drop 1 life (KB/Sec) 4509189/281

On another words, encrypted packets were sent by R2 but were not delivered to R1.

What's going wrong?

crypto ACLs on R1 and R2 are mirrored.

R2:

permit tcp host 172.23.250.13 eq 5023 any

R1:

permit tcp any host 172.23.250.13 eq 5023

and command (sh access-l) shows that traffic was matched on R1 and R2.

P.S. Without IPSEC TCP session can be established, so it's not routing or something else.

wong34539 · ‎06-20-2007

most common reasons is if a router, PIX Firewall, ASA or VPN Concentrator loses dead peer detection (DPD) keepalives on the path.

DPDs are used in order to verify if the remote peer still answers, because it is unsafe to keep a connection active if the remote device is dead. To a device that loses these packets, it means that the peer no longer responds to ACK for DPD, and therefore, is not reachable.

The Internet Key Exchange (IKE) keepalive packets are sent every 10 seconds, by default. Once three packets are missed, an IPsec termination point concludes that it has lost connectivity with its peer.

In order to resolve this issue, issue the crypto isakmp keepalive command on the Router. This allows the gateway to send DPD messages to the peer.