4 Hop routing result in a TTL = 1

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Aug 13th, 2008
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Hi


Im troubleshooting a strange phenomen in our Routed campus LAN, wich consist basically of 6500 with CatOS and MSFC2 with IOS 12.1 / 12.2 and OSPF as routing protocoll.

Here is the cenario:


From a given source to a given destinageion there are 4 hops. Each steps from the source to the destination has been verified, and there are only one route to each. The routes hasn't changed the last 24 hours on any of the involved routers.


When i ping from the source to the destination, and connects a sniffer to the same port as the desionation host is connected, i see TTL=1 in the echo packet.


The real problem is actually that the connectivity is intermitted. Sometimes the last router sends a icmp-dest unreachable and sometimes i can see tha icmp-echo reply from the destination host (with a TTL=64).


Does anyone have an idea or have had simular experiences?


I would be grateful for all answers and tips.

Best Regards

Jarle Steffensen

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massimiliano.se... Wed, 08/13/2008 - 03:41
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Hi,

Did you performed a traceroute? What do you see?


Massimiliano.

jsteffensen Wed, 08/13/2008 - 05:41
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Hi


Ive performed a traceroute also, and it showed that the packets traveled through the expected route.


Jarle Steffensen

Pravin Phadte Wed, 08/13/2008 - 06:48
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Hi,


The source to dest ping which has been noted above is from one device (pc) to the dest device (pc) or may be from router to (pc) and not to the router.


The TTL vaules would not help you much indentifing the problem but only to understand what device is placed on the dest side. The TTL values on the devices can be changed also.


Below are the few list of default TTL.


+--------------------+-------+---------+---------+

| OS Version |"safe" | tcp_ttl | udp_ttl |

+--------------------+-------+---------+---------+

AIX n 60 30

DEC Pathworks V5 n 30 30

FreeBSD 2.1R y 64 64

HP/UX 9.0x n 30 30

HP/UX 10.01 y 64 64

Irix 5.3 y 60 60

Irix 6.x y 60 60

Linux y 64 64

MacOS/MacTCP 2.0.x y 60 60

OS/2 TCP/IP 3.0 y 64 64

OSF/1 V3.2A n 60 30

Solaris 2.x y 255 255

SunOS 4.1.3/4.1.4 y 60 60

Ultrix V4.1/V4.2A n 60 30

VMS/Multinet y 64 64

VMS/TCPware y 60 64

VMS/Wollongong 1.1.1.1 n 128 30

VMS/UCX (latest rel.) y 128 128

MS WfW n 32 32

MS Windows 95 n 32 32

MS Windows NT 3.51 n 32 32

MS Windows NT 4.0 y

128 128


Now about TTL value 1. You may need to check the configs on the device is connected.


Check the below link for more details.


http://www.cisco.com/en/US/docs/ios/12_4t/12_4t2/htaclttl.html


Hope this helps.

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