Ccna routing and Switching Complete Study Guide

telnet 172.16.20.254

Trying 172.16.20.254 ...

% Destination unreachable; gateway or host down

This is some pretty ominous output! Let’s try from R2 and see what happens:

R2#

telnet 172.16.20.254

Trying 172.16.20.254 ... Open

 

User Access Verification

 

Password:

Oh my—I can ping the server from a remote network, but I can’t telnet to it; however, 

the local router R2 can! These factors eliminate the server being a problem since I can 

telnet to the server when I’m on the local LAN.

And we know we don’t have a routing problem because we fixed that already. So what’s 

next? Let’s check to see if there’s an ACL on R2:

R2>

sh access-lists

---

842

 

Chapter 20 

■

  Troubleshooting IP, IPv6, and VLANs

Extended IP access list 110

    10 permit icmp any any (25 matches)

Seriously? What a loopy access list to have on a router! This ridiculous list permits 

ICMP, but that’s it. It denies everything except ICMP due to the implicit 

deny ip any 

any

 at the end of every ACL. But before we uncork the champagne, we need to see if this 

foolish list has been applied to our interfaces on R2 to confirm that this is really our 

problem:

R2>

sh ip int fa0/0

FastEthernet0/0 is up, line protocol is up

  Internet address is 172.16.20.1/24

  Broadcast address is 255.255.255.255

  Address determined by setup command

  MTU is 1500 bytes

  Helper address is not set

  Directed broadcast forwarding is disabled