[j-nsp] Need help on ping output

Guy Davies Guy.Davies@telindus.co.uk
Thu, 14 Nov 2002 17:59:46 -0000

Hi Sonny,

> Hi guy,
> Thanks for replying.
> > The address is the source of the packets being 
> sent back to
> > "router" with ICMP Destination Host Unreachable messages in 
> them.  That
> > means that your packets reached a router which had no route to the
> > destination host.  I suggest that you identify the location of that
> router.
> Is it possible that is denying ICMP and thus 
> return the ICMP Dest
> Host Unreachable? But it somehow allows other traffic 
> (non-ICMP) through?

Unlikely.  Is the same host as the far end of the link

> Could an ACL might cause this kind of ping reply?

No, that would generate a different error.

> In any case, what does each entry mean? (e.g Vr, HL .etc):
> 36 bytes from Destination Host Unreachable
> Vr HL TOS  Len   ID Flg  off TTL Pro  cks      Src      Dst
>  4  5  00 0054 e4db   0 0000  fe  01 2b8d  

Vr -  Version (IPv4)
HL -  Header Length?
TOS - Type of Service byte
Len - Length in bytes
ID -  Fragment ID?
Flg - Flag (fragmentation?)
off - offset (from the beginning of the first fragment?)
TTL - Time to Live (255 in this case)
Pro - protocol? 1=ICMP
cks - checksum
Src - source
Dst - destination

> > You need to check that the interface is actually up and 
> you're not using
> > some alternative path to reach destinations "beyond" your ATM link.
> >
> > I'd also suggest that you check your routing table and 
> forwarding table to
> > see what the next hop for is.  If you don't 
> see it using
> the
> > command "show route <blah>" then try "show route <blah> 
> hidden extensive".
> > That might show you that the route is actually being 
> filtered (perhaps
> > because has been added to your martians?).  
> If this is the
> > case, the packet may be using a default route to reach 
> but, if
> > that router is injecting the default, there will be no 
> forwarding path
> from
> > there.
> There is no other path to reach "show route 
> <blah>" shows
> that the IP is learned via a connected subnet.
> router> show route
> inet.0:
> + = Active Route, - = Last Active, * = Both
>  *[Direct/0] 2d 17:54:22
>                     > via at-0/0/0.6
> I've checked that the route has not been added to the martian list.



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