Ping vs Traceroute

Unanswered Question
Mar 23rd, 2002

Hi,

From my core router, for a paticular IP address, i am able to PING but with Traceroute i am getting unreachability after 5 hops. Why that's occuring?

I am able to ping BGP neighbor loopback address from my LAN system but not able to ping or trace from the core router(in which BGP running).

Thanks in advance...

Regards...

--Ashok.

I have this problem too.
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vikas.arya Sat, 03/23/2002 - 07:40

Dear Ashok,

It might be the case that the router at the sixth hop is phantom router.

reinke Sun, 03/24/2002 - 08:12

Ashok,

cisco routers are using udp packets with a specific desination port. If there is e. g. a well configured firewall on the way to the target, the traceroute will fail.

To validate this assumption just try a traceroute from your windows PC (tracert). The PC do not use udp packets for tracerouting.

Edgar

ashok_boin Tue, 03/26/2002 - 21:14

Hi Reinke,

Thank you very much for your reply. Ok, from PC if it will not use UDP packets, then which Transport protocol is being used by Traceroute, i think the only other option is TCP but it's not for Traceroute.

Thanks in advance...

Rgds...

--Ashok.

srittenberg Tue, 03/26/2002 - 21:28

Windows OS PC uses icmp for trace route. Many firewall may block icmp echo reply. If you really want/need to know the trace, you may use the TCPTraceRoute (Unix base) which is a tcp trace finder that uses TCP SYN packets, instead of the more traditional UDP or ICMP ECHO packets. In doing so, it is able to trace through many common firewall filters.

rampirbux Thu, 03/28/2002 - 04:34

Hi,

in case of trace you could try/use an extended ping with the "record"-route option.

router#ping

Protocol [ip]:

Target IP address: [ipaddress]

Repeat count [5]:

Datagram size [100]:

Timeout in seconds [2]:

Extended commands [n]: y

Source address or interface: [interface or ipaddr]

Type of service [0]:

Set DF bit in IP header? [no]:

Validate reply data? [no]:

Data pattern [0xABCD]:

Loose, Strict, Record, Timestamp, Verbose[none]: R

Number of hops [ 9 ]:

Loose, Strict, Record, Timestamp, Verbose[RV]:

Sweep range of sizes [n]:

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to [ipaddress], timeout is 2 seconds:

Packet has IP options: Total option bytes= 39, padded length=40

this will show you also the paths(both ways) to the destination, with a limit of 9 hops.

Hope this help.

-Ramon Pirbux

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Posted March 23, 2002 at 4:21 AM
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