Re: MTU Issues

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
Blogs and organic groups at http://www.ccie.net