Cisco – Pinging a host from a router through the selected interface

ciscopingrouter

In a typical Cisco router it's possible to ping a host from the router's OS. When the ping packet leaves router (call it R1) through the fa0/0 interface, the source IP of that packet it set to the IP of fa0/0, right?

Is it possible to specify the interface of R1 I want the ping packet to go through? Different interfaces = different source IPs.

I know that usually there's only one way to the destination, but still. I'm not even sure if it's possible, because we would need to somehow make the router ignore its routing table – simply because the routing table gives a router exact information where to send the packet to, there can't be two 'matching' entries with identical priority in the table.

Best Answer

You can set the source of the ping, but the direction is determined by the routing table and rules configured in the router.

You can use PBR to override the routing table, but that does affect the routing speed since it must be done in software. Also, it doesn't scale, and you can end up with routing loops.

Related Solutions

Cisco 1841 – Configuration Issue with NAT

first of all you have a duplex mix match. if you are wanting to do at test to make your configuration work i would recommend that you make both interfaces duplex auto (in addition to your speed). i would also change your inside outside overload statement to have your inside traffic pointing towards the outside interface. ie. ip nat inside source list 101 interface fastethernet 0/1 overload try this and see if it gets you access.... in 3 years

Cisco – Can you ping a Cisco Router’s Loopback Interface from a PC using PacketTracer

As with the loopback interface on your PC, loopback interfaces on Cisco devices are local to those devices only. In order to reach the loopback IP, you must have some route to it via the Cisco device in question.

In your example, you would need to give the router an address on Fa0/1 and put the PC in the same subnet (not the same subnet as the loopback interface). The PC will then need a route to the loopback IP via the 1841. This can be a default route, or a more specific route, just so long as the PC knows that it had to get to the 1841's loopback IP via the 1841's Fa0/1 IP.

For example:

! Change the IP here and use a /32 netmask
interface Loopback0
 ip address 192.168.255.1 255.255.255.255

! give the old Loop0 IP to Fa0/1
interface FastEthernet0/1
 ip address 192.168.254.1 255.255.255.0

Your PC already has an address inside 192.168.254.0/24, so all you need to do is configure its default gateway as 192.168.254.1. The PC should now be able to ping the 1841's loopback IP, 192.168.255.1.

Best Answer

Related Solutions

Cisco 1841 – Configuration Issue with NAT

Cisco – Can you ping a Cisco Router’s Loopback Interface from a PC using PacketTracer

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