Re: MTU Issues

i dont have packet capture,this message i won't be getting on my telnet
session.i have read on internet i shld receive this
message.

Customer complaints that TCP files transfered from B to A with MTU 1500 has
no problem but from A to B it can't above 1492. He says that the problem is
with the customer carrier not with the backbone carrier.

How the above para can be possible,traffic is passsing through the same
interface as such what it is passing from to A to B

On Tue, Oct 6, 2009 at 11:10 PM, Bryan Bartik <bbartik_at_ipexpert.com> wrote:

> You won't get a Destination Unreachable, you will get a Fragmentation
> Needed and Don't Fragment Bit Set. Did you get a packet capture? Who is
> sending you the message?
>
>
> On Tue, Oct 6, 2009 at 1:01 PM, mike arnold <haynessmith70_at_gmail.com>wrote:
>
>> Hello Dear,
>>
>> Yes it is a straight ethernet,and i have not changed anything on interface
>> configs on DS/PE facing to customer A,it is default to 1500,customer is
>> complaining that he can't transfer TCP files larger than 1492 from
>> A----B. But he says that he is able to transfer TCP files from B----A
>> with larger size than 1492. He says that there is no problem with backbone
>> carrier but with the customer carrier.
>>
>> When i do a extended ping from mine DS/PE to customer B with a DF bit
>> set the ping sucess is 0% for larger MTU also i dont recieve any error
>> saying ICMP destination unreacheable messages,
>>
>> Generally when a MTU is high and DF is set the intermediate router send a
>> notification ICMP destination unreacheable messages,but in my case no
>> feedback except success rate.
>>
>> On Tue, Oct 6, 2009 at 10:36 PM, Bryan Bartik <bbartik_at_ipexpert.com>wrote:
>>
>>> Well make sure it raised on ALL the core links. Is the link between the
>>> CE and PE straight Ethernet? 1500 should be fine there.
>>>
>>>
>>> On Tue, Oct 6, 2009 at 12:32 PM, mike arnold <haynessmith70_at_gmail.com>wrote:
>>>
>>>> Hello,
>>>>
>>>> The link on distribution PE facing to customer A is default to MTU
>>>> 1500,on distribution to core it is mpls mtu 1524 and SVI on core facing to
>>>> ISP is default to 1500 on ethernet.
>>>>
>>>>
>>>>
>>>> On Tue, Oct 6, 2009 at 10:15 PM, Bryan Bartik <bbartik_at_ipexpert.com>wrote:
>>>>
>>>>> Did you raise the MTU on the other links?
>>>>>
>>>>> On Tue, Oct 6, 2009 at 12:02 PM, mike arnold <
>>>>> haynessmith70_at_gmail.com> wrote:
>>>>>
>>>>>> Hello Dear's
>>>>>>
>>>>>> Topology:
>>>>>>
>>>>>> Its a Carrier Supporting Carrier Scenario.
>>>>>>
>>>>>> A------DS/PE---CORE/P---ISP/PE--P---ISP/PE------B
>>>>>>
>>>>>> AS per above topology,am not able to transfer files with MTU frame
>>>>>> size
>>>>>> above 1492 though the MTU configured on interface is 1500.The
>>>>>> interface on
>>>>>> which customer A is connected MTU is default to 1500.The link between
>>>>>> DS/PE---CR/PE is mpls enabled i have configured the MTU size to 1524
>>>>>> to
>>>>>> carry labels of MPLS as recommended by cisco.
>>>>>>
>>>>>> When i do extnded ping from DS/PE above MTU size of 1492 with even DF
>>>>>> bit
>>>>>> not set am not able to ping customer end (B),
>>>>>>
>>>>>> AND also i tried with DF bit set am not able to recieve any
>>>>>> notifications
>>>>>> ICMP destination unreacheable messages.
>>>>>>
>>>>>> The file transfer from customer B with packet size above 1492 are
>>>>>> received
>>>>>> by customer A but when the connection are initiated through customer A
>>>>>> they
>>>>>> are not.
>>>>>>
>>>>>> Within an enterprise it works with larger MTU size when tried to ping
>>>>>> from
>>>>>> Distribution loopback to core loopback.How can i troubleshoot it is a
>>>>>> problem through my end or from the ISP.
>>>>>>
>>>>>> The link between core and ISP is back to back VRF connected via a
>>>>>> layer 2
>>>>>> trunk.The ISP is creating a sub-interfaces on his 3800 router with
>>>>>> encapsulation and vlan number.AND on Core am creating a SVI with a
>>>>>> same vlan
>>>>>> number and ip address within the subnet.
>>>>>>
>>>>>> Each customer VRF for exampl:(Customer A) is associated with SVI
>>>>>> virtual
>>>>>> interface on 6500(core)and traffic is passed to customer B.On SVI the
>>>>>> MTU is
>>>>>> default to 1500.
>>>>>>
>>>>>> BGP is routing protocol between CORE nd ISP.
>>>>>>
>>>>>> ON 3800 router (ISP End)
>>>>>> int gig0/0
>>>>>> no shut
>>>>>> no ip add
>>>>>>
>>>>>> int gig0/0.1
>>>>>> no shut
>>>>>> encapsulation dot1q 50
>>>>>> ip vrf forwarding XX
>>>>>> ip add 10.10.10.1 255.255.255.254
>>>>>>
>>>>>> ON MY END (CORE)
>>>>>> int gig5/1
>>>>>> switchport trunk encapsulation dot1q
>>>>>> switch mode trunk
>>>>>>
>>>>>> int vlan 50
>>>>>> ip vrf forwarding customer A
>>>>>> ip add 10.10.10.2 255.255.255.254.
>>>>>>
>>>>>> Thanks
>>>>>>
>>>>>>
>>>>>> Blogs and organic groups at http://www.ccie.net
>>>>>>
>>>>>>
>>>>>> _______________________________________________________________________
>>>>>> Subscription information may be found at:
>>>>>> http://www.groupstudy.com/list/CCIELab.html
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Bryan Bartik
>>>>> CCIE #23707 (R&S), CCNP
>>>>> Sr. Support Engineer - IPexpert, Inc.
>>>>> URL: http://www.IPexpert.com <http://www.ipexpert.com/>
>>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> Bryan Bartik
>>> CCIE #23707 (R&S), CCNP
>>> Sr. Support Engineer - IPexpert, Inc.
>>> URL: http://www.IPexpert.com <http://www.ipexpert.com/>
>>>
>>
>>
>
>
> --
> Bryan Bartik
> CCIE #23707 (R&S), CCNP
> Sr. Support Engineer - IPexpert, Inc.
> URL: http://www.IPexpert.com <http://www.ipexpert.com/>

Blogs and organic groups at http://www.ccie.net
Received on Tue Oct 06 2009 - 23:21:50 ART