Recently I had to troubleshoot a problem with Cisco TAC. Engineer asked me to draw my scheme in this very cool service. Check it out @ asciiflow
How to see if your router is under heavy VPN traffic? Configure netflow export and enter following command:
router# sh ip cache flow | i _32_.+
Recently I had a situation where customer asked me to configure remote access VPN on his old Cisco 871. Configuration was quite simple but I had problem with connecting iPhone to his network.
The solution is quite simple: apparently Apple doesn’t like 3des so I had to configure transformset like this:
crypto ipsec transform-set myset esp-aes 256 esp-sha-hmac
check your MTU settings with
user@computer:~$ tracepath -n www.cix.hr
1: 10.254.30.250 0.099ms pmtu 1500
1: 10.254.30.254 0.425ms
1: 10.254.30.254 0.405ms
2: 10.0.0.1 1.345ms
3: 188.8.131.52 4.111ms
4: 10.51.0.2 4.327ms
5: 10.50.0.74 192.967ms
6: 184.108.40.206 6.561ms asymm 7
7: 220.127.116.11 4.719ms asymm 10
8: 18.104.22.168 6.181ms asymm 9
9: 22.214.171.124 5.390ms asymm 10
10: 126.96.36.199 4.403ms reached
Resume: pmtu 1500 hops 10 back 54
3CDaemon. Download it here.
my customer is peering with 2 ISP’s and has configuration with 2 BGP routers mutually connected with iBGP.
routers are reciving full tables from ISP’s and has 4 byte AS (XXXXXX).
recently we noticed that BGP session between customer and ISP2 is constantly flapping each 3 minutes. logs didn’t show anything useful
%BGP-4-MSGDUMP: unsupported or mal-formatted message received from X.X.X.X
I searched cisco forums and tried to isolate problem by inserting hidden command “neighbor X.X.X.X dont-capability-negotiate”.
%BGP-3-NOTIFICATION: received from neighbor X.X.X.X active 2/2 (peer in wrong AS) 2 bytes 5BA0
by reading this article I assumed that ISP is announcing itself with wrong AS.
problem was finally solved by entering command in global configuration mode (and removing dont-capability-negotiate)
ip tcp mss 1440
To learn something more about TCP MSS go here.
easy tutorial @ thegeekstuff.
program for scanning networks for NetBIOS name information
nice document on Cisco site