Cisco 1721 router IPSec Issues

Posted on 2009-07-14
Last Modified: 2012-05-07
I have a Cisco 1721 router, with current IOS c1700-k9o3sy7-mz.122-11.T.bin

Everything is up and running fine, minus anything IPSec.

When the IPSec is setup it seems to refuse to pass traffic over the tunnel we create.  Absolutely no debugging information is show as well with the debug turned on.  Even after trying with multiple devices on the other side, still, no luck.

Here is my config (IP and names modified) and what the show crypto ipsec sa produces

Current configuration : 1719 bytes
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
hostname contoso
boot system flash:c1700-bk9no3r2sy7-mz.122-13.T.bin
enable secret
enable password contoso
ip subnet-zero
ip dhcp excluded-address
ip dhcp pool contoso
   lease 7
ip audit notify log
ip audit po max-events 100
crypto ca trustpoint verisign-ca
 enrollment url http://ciscoca-ultra:80
crypto isakmp policy 10
 encr 3des
 hash md5
 authentication pre-share
 group 2
 lifetime 3600
crypto isakmp key contoso address
crypto ipsec transform-set contoso esp-3des esp-md5-hmac
crypto map contoso 10 ipsec-isakmp
 set peer
 set transform-set contoso
 match address 105
interface FastEthernet0
 description inside
 ip address
 ip nat inside
 speed auto
interface Serial0
 description Gateway
 ip address
 ip nat outside
 crypto map contoso
ip nat inside source route-map contoso interface Serial0 overload
ip classless
ip route Serial0
no ip http server
access-list 105 permit ip
access-list 175 deny   ip
access-list 175 permit ip any
route-map contoso permit 1
 match ip address 175
line con 0
line aux 0
line vty 0 4
 password contoso
no scheduler allocate
contoso#show crypto ipsec sa
interface: Serial0
    Crypto map tag: contoso, local addr.
   local  ident (addr/mask/prot/port): (
   remote ident (addr/mask/prot/port): (
     PERMIT, flags={origin_is_acl,}
    #pkts encaps: 0, #pkts encrypt: 0, #pkts digest 0
    #pkts decaps: 0, #pkts decrypt: 0, #pkts verify 0
    #pkts compressed: 0, #pkts decompressed: 0
    #pkts not compressed: 0, #pkts compr. failed: 0, #pkts decompress failed: 0
    #send errors 0, #recv errors 0
     local crypto endpt.:, remote crypto endpt.:
     path mtu 1500, media mtu 1500
     current outbound spi: 0
     inbound esp sas:
     inbound ah sas:
     inbound pcp sas:
     outbound esp sas:
     outbound ah sas:
     outbound pcp sas:

Open in new window

Question by:MainStaySolutions
  • 5
  • 4

Expert Comment

ID: 24849928
Can you show the output of a "Show crypto isakmp sa" and "Show ip nat trans"
LVL 28

Expert Comment

by:Jan Springer
ID: 24849941
Is the access-list (105) an exact inverse match of the one listed above?

Do the encryption and hash match?

Author Comment

ID: 24850049
Here is the output of the two commands.

contoso#show crypto isakmp sa
dst             src             state           conn-id    slot
contoso#show ip nat trans

Open in new window

Create the perfect environment for any meeting

You might have a modern environment with all sorts of high-tech equipment, but what makes it worthwhile is how you seamlessly bring together the presentation with audio, video and lighting. The ATEN Control System provides integrated control and system automation.


Author Comment

ID: 24850494
You mean for the other side?

The only thing that is slightly different that instead of it being a class C subnet like the router shows it's actually a class B subnet.

All the encryption protocols do match.  We even tried instead of 3DES, DES.  And still nothing.
LVL 28

Expert Comment

by:Jan Springer
ID: 24850744
The access lists need to be an *exact* inverse match of each other as applied to the crypto peer config.

Author Comment

ID: 24851979
Everything now matches, and still no luck.
LVL 28

Expert Comment

by:Jan Springer
ID: 24852158
term mon
debug crypto isakmp
debug crypto ipsec

sh crypto isakmp sa
        -> show SAs between two peers

sh crypto ipsec sa
        -> show IPsec SAs built between peers

sh crypto engine connection active
        -> show each phase 2 SA built

Author Comment

ID: 24853627
Okay, after much fighting the tunnel is up, however, I can't ping anything on the other side now.
LVL 28

Expert Comment

by:Jan Springer
ID: 24853724
What did debug and/or the log data indicate?

Accepted Solution

MainStaySolutions earned 0 total points
ID: 24935141
We got it figured out.  The issue was with the device on the other side.  

Featured Post

Watch Anatomy of a Wi-Fi Hack On-Demand

In less than a weekend, anyone with Internet access and some free time can become a Wi-Fi MitM to wreak havoc on your network. View our Wi-Fi Expert in an on-demand episode of our Secure Wi-Fi mini-series as he explores the motives, execution, and anatomy of a Wi-Fi hack.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
home router to use as repeater  (signal extender) 10 64
ip igmp join-group 8 68
Grant drive/folder change permissions to VPN user 6 29
Port# 500 and 4500 not open by ISP 10 44
The Cisco RV042 router is a popular small network interfacing device that is often used as an internet gateway. Network administrators need to get at the management interface to make settings, change passwords, etc. This access is generally done usi…
Creating an OSPF network that automatically (dynamically) reroutes network traffic over other connections to prevent network downtime.
After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
Windows 10 is mostly good. However the one thing that annoys me is how many clicks you have to do to dial a VPN connection. You have to go to settings from the start menu, (2 clicks), Network and Internet (1 click), Click VPN (another click) then fi…

713 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question