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Pinging interfaces from the Console

Can anyone point me to good documentation about general rules and limits for using ip ping to test basic fuctionality of Cisco routers by pinging interfaces from the console? Recently, on a Cisco 800 ISDN router, I was unable to ping the BRI0 interface at all and can ping eth0 only if I have no access-list attached or the access list allows icmp. I had incorrectly assumed that any functioning ip interface could be pinged from the console. The router fuctioned fine after the ISP fixed their end. I am also wondering if the ability to ping ethernet interfaces from the console varies depending on the model of router or are the rules the same for all IOS versions regardless of the router type? I haven't encountered this problem with PIX firewalls.

I have searched numerous times for definitive answer but keep coming up short.

Thanks,

Rich

1 REPLY
Cisco Employee

Re: Pinging interfaces from the Console

Rich,

I wasnt able to find a document that specifically discusses pinging from console but let me try and explain.

When you generate an ICMP Packet from the router for a specific destination, the ICMP Packet is sourced from the interface that has the best routing path to the destination. So, in your case when you are consoled into the router that generate an ICMP packet to the Ethernet0, since the network is directly connected, the packet is sourced from the Ethernet0 itself. And if you have an ACL denying ICMP Traffic, then you will not be able to ping.

For example:

interface GigabitEthernet0/0

ip address 10.89.245.56 255.255.255.0

ip access-group 100 in

no ip route-cache cef

duplex auto

speed auto

ntp disable

end

2821#sh deb

Generic IP:

IP packet debugging is on for access list 100

2821#sh access-lists

Extended IP access list 100

10 deny ip any any log

2821#

Debug while Pinging from Console:

2821#ping 10.89.245.56

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.89.245.56, timeout is 2 seconds:

.

*Oct 19 15:36:47.746: %SEC-6-IPACCESSLOGDP: list 100 denied icmp 10.89.245.56 ->

10.89.245.56 (0/0), 8 packets

Success rate is 0 percent (0/5)

2821#

I hope the below document answers some of your question on ICMP.

Understanding the Ping and Traceroute Commands

http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_tech_note09186a00800a6057.shtml

Let me know if it helps.

Regards,

Arul

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