Redundant ISP - check connectivity

pestebogdan · ‎04-03-2009

Hy experts,

I have the following configuration: a 1841 Cisco Router, IOS ver 12.3(4) and two internet providers, each configured with it's own public IP, which is NATed.

I used "route-maps", so is the primary connection goes down (in the sense that the L1 connection goes down (broken cable, pull cable out), the redundant ISP connection is automatically inserted in the ROUTE TABLE.

All fine and dandy, except that when the internet "goes down", 99.9% of the time it's because of the ISP's Gateway Problem (not a switchport problem), so even if the Internet goes down, the backup connection doesn't activate, unless i manually remove the cable from the router.

What i want to do is base this "redundant ISP plan" on ICMP packets..so if the gateway dowsn't respond to pings for x seconds, activate the backup route and keep monitoring until the connection comes back up.

Any suggestions ?

Thanks.

Jon Marshall · ‎04-03-2009

Bogdan

You need to look at "ip sla .." functionality. Have a look at this recent thread which should get you started -

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=WAN%2C%20Routing%20and%20Switching&topicID=.ee71a06&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40^1%40%40.2cd28669/2#selected_message

Edit - Bogdan, apologies but i'm having problem copying the link. In the search NetPro box type "ip sla" and then it's the 5th entry marked "2 Gateways, route-map and OSPF"

Jon

pestebogdan · ‎04-03-2009

Hi Jon,

Thanks for the answer. The solution provided above seems to be what i am looking for, but my cisco 1841 dowsn't seem to have the ip sla command, which is odd because looking at the IOS command list, it should be there.

Here is the output of the #show version command:

Cisco IOS Software, 1841 Software (C1841-IPBASE-M), Version 12.4(3i), RELEASE SOFTWARE (fc2)

Technical Support: http://www.cisco.com/techsupport

Compiled Wed 28-Nov-07 18:17 by stshen

ROM: System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)

BDO uptime is 6 hours, 28 minutes

System returned to ROM by reload at 13:05:21 UTC Fri Apr 3 2009

System image file is "flash:c1841-ipbase-mz.124-3i.bin"

Cisco 1841 (revision 7.0) with 114688K/16384K bytes of memory.

Processor board ID FCZ130793CU

6 FastEthernet interfaces

DRAM configuration is 64 bits wide with parity disabled.

191K bytes of NVRAM.

31488K bytes of ATA CompactFlash (Read/Write)

Configuration register is 0x2102

Could anyone explain why the router doesn't recognize the R(c)#ip sla statement ?

Thank you

Edison Ortiz · ‎04-03-2009

Not supported under IP Base.

You need either SP Services, Advanced IP Services or Enterprise for IP SLA support on this router.

I recommend getting Advanced IP Services but be aware of the software licensing cost.

__

Edison.