All,
I am facing a similar issue and did some preliminary research. Hope you have
already tried this!?
1. PMTU Black hole detection on the NT Server
2. Upgrade the NT server to latest Service Pack
3. Verifying that ICMP unreachable are reaching back to the NT Server
4. Decreasing the MTU size on NT server
5. Increasing the MTU size on the Routers
Out of the above option 4 and 5 depends/impacts the other system an LAN and
WAN. But option 1, 2 and 3 can be tried. The following links provide
sufficient information to implement the same.
Why Can't I Browse the Internet when Using a GRE Tunnel?
http://www.cisco.com/warp/public/105/56.html
PMTU Black Hole Detection Algorithm Change for Windows NT 3.51
http://support.microsoft.com/support/kb/articles/q136/9/70.asp
Adjusting IP MTU, TCP MSS, and PMTUD on Windows and Sun Systems
http://www.cisco.com/warp/public/105/38.shtml
Windows TCP/IP Registry Entries
http://support.microsoft.com/support/kb/articles/q158/4/74.asp
Vijay
>From: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>Reply-To: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>To: "Donohue, Steve" <[EMAIL PROTECTED]>, "'Phil Barker'"
><[EMAIL PROTECTED]>, "Gareth Hinton"
><[EMAIL PROTECTED]>, [EMAIL PROTECTED]
>Subject: RE: Not receiving ICMP messages
>Date: Wed, 25 Oct 2000 11:44:15 -0700
>
>At 07:36 AM 10/25/00, Donohue, Steve wrote:
>
>>I found this link as well that is why I am wondering about the lack of
>>ICMP
>>messages. I realize that when you enable HSRP on an interface it disables
>>ICMP redirects. Would the ICMP messages requesting a smaller MTU size
>>fall
>>under this category?
>
>No (unless there's a bug, which I haven't heard is the case)
>
>
>>Thanks again all.
>>
>>Steve
>>
>>-----Original Message-----
>>From: Phil Barker [mailto:[EMAIL PROTECTED]]
>>Sent: Wednesday, October 25, 2000 7:22 AM
>>To: Gareth Hinton; [EMAIL PROTECTED]
>>Subject: Re: Not receiving ICMP messages
>>
>>
>>Gareth,
>> This is a better link.
>>
>>http://www.cisco.com/warp/public/105/56.html
>>
>>HTH,
>>
>>Phil.
>>
>>--- Gareth Hinton <[EMAIL PROTECTED]>
>>wrote: > Hi Steve,
>> >
>> > Is the MTU size of 1476 a limitation of the
>> > encryption, or merely because of
>> > the overheads added by the encryption knocking it
>> > down from 1500. Is it a
>> > possibility to increase the MTU size on the link?
>> >
>> > Gaz
>> >
>> > "Phil Barker" <[EMAIL PROTECTED]> wrote in
>> > message
>> >
>>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
>> > > Steve,
>> > > Without CLI access your going to struggle.
>> > > Q : How far does the traceroute get, from the send
>> > > node ?
>> > >
>> > > try rfc 792 ICMP
>> > > http://www.landfield.com/rfcs/rfc792.html
>> > >
>> > > >> SNIP from RFC 792
>> > >
>> > > If a host reassembling a fragmented datagram
>> > > cannot complete the
>> > > reassembly due to missing fragments within
>> > its
>> > > time limit it
>> > > discards the datagram, and it may send a
>> > time
>> > > exceeded message.
>> > >
>> > > If fragment zero is not available then no
>> > time
>> > > exceeded need be
>> > > sent at all.
>> > >
>> > > Good luck,
>> > >
>> > > Phil.
>> > >
>> > >
>> > >
>> > > --- "Donohue, Steve" <[EMAIL PROTECTED]>
>> > wrote:
>> > > > Good Afternoon All,
>> > > >
>> > > > I am currently trying to resolve an issue where
>> > we
>> > > > are having trouble
>> > > > sending data across a tunnel running GRE
>> > encryption.
>> > > > With this encryption
>> > > > employed the MTU size allowed is decreased to
>> > 1476.
>> > > > When we attempt to send
>> > > > traffic (email, ftp, etc...) through the tunnel,
>> > we
>> > > > are finding that it does
>> > > > not work.
>> > > >
>> > > > My sniffer trace is showing that the frames
>> > being
>> > > > sent are setting the DF
>> > > > bit, which I would expect. I would then expect
>> > that
>> > > > if the router is unable
>> > > > to send the packet, it would drop it and return
>> > an
>> > > > ICMP message back to the
>> > > > source telling it to decrease the packet size
>> > and
>> > > > try it again. I am not
>> > > > seeing any of these messages.
>> > > >
>> > > > We are running HSRP on the ethernet interfaces
>> > that
>> > > > connect to my LAN. I
>> > > > believe we are running a 12.0 IOS release,
>> > although
>> > > > I am not sure of the
>> > > > actual version.
>> > > >
>> > > > Does anyone have any ideas why this might be
>> > > > happening? I am trying to
>> > > > resolve this issue while having no CLI access to
>> > the
>> > > > routers. I have been
>> > > > informed by the controlling body that there are
>> > no
>> > > > access lists prohibiting
>> > > > ICMP messages from being sent, and there are no
>> > > > firewall rules in place that
>> > > > would be dropping the ICMP messages.
>> > > >
>> > > > Any and all explanations of possible
>> > > > causes/resolutions would be
>> > > > appreciated.
>> > > >
>> > > > Steve D.
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > >
>> > >
>> > >
>> >
>>____________________________________________________________
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