Layer 3 Etherchannel and MPLS MTU

Greetings,
If two 7609 are connected through layer 3 giga etherchannel and 7609-1 sends a frame with 1514 bytes plus two MPLS header to 7609-2, does the command mpls mtu 1522 under the giga etherchannel interface on both routers is enough?
Or it is necessary to add the global command system jumbomtu 1522 and the interface command mtu 1522 under physical gigainterfaces participating on the channel?
Cisco docs say many platforms will accept frames higher than 1500 bytes (up to 24 bytes) to accommodate control flags; that is why I am considering just mpls mtu xxx is enough.
Also, reading Cisco doc I understood that system jumbomtu xxxx and mtu xxxx should be used together. I tested sending frames higher than 1514 bytes (without MPLS tags) and system jumbomtu xxxx alone was not enough, ping failed; it was necessary to add mtu xxxx under the interface. Do you have a different experience?
Thanks,
Alaerte Gladston Vidali
IBM Global Services - SO
Tel.55+11+2121-2879 Fax:55+11+2121-2449

Hi
We had some peculiar exp with 7600 (7609/7606) boxes in which we did change the physical mtu of the interface instead of mpls mtu.
Again that did the trick for us even in 7200 where we monitored the same kinda behaviour..
regds

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Pmtu and interface mtu,mpls mtu

Hi,
If pmtu work , do i need config interface mtu and mpls mtu on interface facing core,or p-p along the path.
thank you!

Not necessarily. However, Path MTU is not guaranteed to work all the time because of things like firewalls and access-list. From a performance perspective, you will want the maximum possible MTU, which is what makes it adviseable to change the MTU (IP/MPLS).

MTU over DMVPN and MPLS

Hello All,
I have a query regarding MTU over both DMVPN and MPLS.
I have been running the following command from a windows box
ping x.x.x.x -f -l yyy (yyyy being the buffer size) and x.x.x.x being my remote hosts
I am using the same destination host and have two different paths to it. One over MPLS and one over a DMVPN.
I would have expected to be able to send packets with a higher MTU over the MPLS but for both MPLS and DMVPN the maximum packet size I can send with the DF bit set is the same (1372).
Is this normal behaviour? I though MPLS would have less overhead, so my maximum packet size would be higher in my tests

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Generally, MPLS supports an increased MTU, when adding MPLS labels, while VPN tunnels, like DMVPN, don't exceed original MTU, and so, it reduces payload space. So, normally, you should see larger ping buffer DF support across MPLS than DMVPN. However, "normal" can be very much impacted by actual device configurations, including making MTU for DF packets the same for either MPLS or DMVPN. (For example, you might want to make the two paths alike so flows that for any reason need to be redirect from one media path to the other see a consistent MTU.)

EtherChannel and LAN Design for new buildiing(s)

What is the recommended best practice for EtherChannel size for a 3750G-12S stack? Will I benefit from stacking these with the StackWise cable on the backplane, or would it be better to run these independently back to the 4006 with individual EtheChannels?
The 3750G-12S stack will likely be 1 or 2 devices at distribution layer for upwards of 18 - 20 2960G-48 access layer switches and approximately 20 1242LAP AP's in addition to max capacity of end users attached to the switches.
I am considering implementing a 4 gig EtherChannel between the 3750's to the 4006 for this load. My limit is the number of available ports on the 4006 and obviously the max load of links on the EtherChannel.

Unsure there's a single "best practice" for stacking or not. Some advantages/disadvantages to both. Part of the decision might rest on whether the 3750s will be L2 or L3.
Stackwise could be a performance bottleneck if you believe there would be much traffic between switch ports, but if most will transit your 4006, your links to it would be the bottleneck.
What you might consider, a single 3750G-12S (four?) that can handle 2 links from each access switch, that are Etherchanneled and not connected to the same 3750 stack member. This with the 4 gig Etherchannel to the 4006, which again should be spread across stack members.

Confused about mpls mtu command

hi,
i confuse about mpls mtu command
test platforms are 76 pfc3b,mpls,gigabit sip400 spa interface
if i didn't config mpls mtu command ,using default,ping command is successful,if more than 1496 packets, i can see fragment from show ip traffic.
if i config mpls mtu override 1504,ping command is sucessful too. there is fragment too when i use 1501 byte packet.
if i config mpls mtu override 1524 byte.
ping command failed if i use packet more than 1500, , all packet are droped,even 1501 byte.only 1500 byte packet can success.
all config above interface mtu is 1500.
this confused me.
why i use default 1500 interace mtu, mpls mtu override 1504 ,ping packet can fragment,ping success, but i use mpls mtu override 1524, i can see fragment in show ip traffic,but ping command failed. i can't see packet in destination router,how this work.
thank you!
jun

topology is simple
7609-1--sip GE spa----7609-2--pos---7609-3--flexwan E1-----7604-1--ge--ce
i config mpls mtu 1524 between 7609-1 and 7609-2 . and keep interface mtu 1500 default.
ping packet from 7609-1 to 7604-1 loopback 0.
ping 1500 byte packet is ok, but ping 1501 byte packet is totally lost.then i config mtu 1524 between 7604-1 and 7609-3, it is useless,notwork, i can't see packet coming from 7609-1 on 7604-1.
but i add config mtu 1524 between 7609-1 and 7609-2. config mtu 1500 between 7604-1 and 7609-3,ping 1501 bytes from 7609-1 to 7604-1 loopback0 is ok. but i can see fragment from show ip traffic command in 7609-3.
i have a question, why we need mpls mtu command. if we don't change interface mtu,just only config mpls mtu 1524, it doesn't work, if we just change mpls mtu,how it work in the ios. if we config interface mtu 1524,interface mtu size is big enough, it seems mpls mtu command is useless, we don't need mpls mtu command, just interface mtu 1524 is ok.
why we need mpls mtu command. we just only change interface mtu is enough.
thank you!
jun

WCCP-2 and MPLS

Hi
This is a question regarding WCCP-2 and MPLS as well.
I have a customer who has Cisco Catalyst 6500 switches and would also like to run MPLS on the Network. MPLS as such is supported only on the Layer-3 modules. The customer has the GIG OSM modules and ATM modules in the switch. The GIG Modules connect to the Internet and the ATM modules connect to various of the branches. The Content Engines are connected to FastEthernet modules on the 6500 which do not support MPLS.
Now to run WCCP-2 redirection, this would be done on the GIG interfaces with the "ip wccp redirect out" command on that interface in addition to the usual commands for WCCP-2. Now what happens is that the input packets received via the branches are all going to be MPLS tagged. Will these packets be redirected to the CE before they are sent off the output GIG interfaces.
Also the customer require to run IP spoofing with WCCP-2. Will the same thing happen in the opposite direction.
Will this work at all.
Thanks

You described the physical connection, but not logical structure.
1. You did not mentioned does the customer have Layer 3 module installed in Catalyst 6500? Catalyst 6500 without RSM (route switch module) can not make desition on the 3d layer.
All modules that you mentioned are 2d layer modules. Usually, when you have RSM, you create virtual interfaces, where you configure the routing or 3d layer information. Of course, you can configure it directly in the physical interface (you need to allow this fuction, by default, physical interfaces are switched ones).
2. Catalyst 6500 - what role it has in MPLS network (CE, PE, something else)?
3. What you mean under "sent to Internet"? Usually the packets to Internet are sent without MPLS tags. MPLS tags are used inside of MPLS backbone. The customer also receie pure IP-packet without any addtional tags.

MPLS MTU on FE interfaces with fixed interface MTU

What is the recommendation for setting MPLS MTU when the hardware does not permit the setting of the interface MTU:
PE-Edge-2(config)#int fastEthernet 0/0
PE-Edge-2(config-if)#mtu 1524
% Interface FastEthernet0/0 does not support user settable mtu.
The MPLS MTU could be changed with "mpls mtu 1524", but this gives the error:
PE-Edge-2(config-if)#mpls mtu 1524
*Dec 24 20:54:43.467: %TFIB-3-MPLS_MTU_SET: Setting mpls mtu to 1524 on FastEthernet0/0 which is higher than the interface mtu 1500 . This could lead to packet forwarding problems including packet drops.
Is it permissible to set the MPLS MTU greater than the interface MTU, as I thought that MPLS packets cannot not be fragmented, but rather simply dropped?
In this scenario, is the only solution to limit the size of inbound packets with something like "ip tcp adjust-mss 1476" to avoid any potential packet drops?

if your doing AToM then you have to change the mpls mtu in order to transport full frames over your backbone. I have the same issue with the mtu and setting the mpls mtu to 9196 while leaving the mtu at 1500 did not impact regular traffic at all but it did allow our l2vpn's to function correctly.

MPLS MTU issue (diagram attached)

Dear Experts ,
I'm trying to run MPLS between two 7206 vxr router which is connected behind a Foundry Big Iron L3 router which is configured as a L2 device .
I put on my 7206 as
int gi0/1
ip address 172.16.14.1 255.255.255.0
mpls ip
mpls mtu 1526
But it seems that there is tag assiging ,but traffic like https didn't work after that . is there is any clue ?
Regards
Haris

Hi ,
There is no way to increase the MTU size on foundry . But it's giving me some error
BigIron1(config-if-e1000-1/8)#ip mtu 1526
Error - 1526 not between 576 and 1500
BigIron1(config-if-e1000-1/8)#mtu ?
Unrecognized command
How can know that whether the foundry supporting giant packets / not ? . I think it's not supporting giants , the following is the output of ping sweep from one cisco router to other one .
If it's not supporting giants what will happens to my mpls packets with size 1508 ? . Is it possible me to put the command "mpls mtu 1500" ,so that mpls mtu will limit to 1500
router1#ping
Protocol [ip]:
Target IP address: 213.12.90.1
Repeat count [5]: 1
Extended commands [n]: y
Source address or interface: 213.12.83.137
Set DF bit in IP header? [no]: y
Sweep range of sizes [n]: y
Sweep min size [36]: 1450
Sweep max size [18024]: 1550
Sweep interval [1]:
Type escape sequence to abort.
Sending 101, [1450..1550]-byte ICMP Echos to 213.12.90.1, timeout is 2 seconds:
Packet sent with a source address of 213.12.83.137
Packet sent with the DF bit set
Success rate is 45 percent (46/101), round-trip min/avg/max = 20/44/120 ms
the ping is same with and without DF bit set after enabling MPLS . But before enabling tag switching as I remember I was able to ping without DF Bit set
Regards
Haris

MPLS MTU size

Hello,
Please correct me if I am wrong. The MPLS MTU size is 1518 to 1520 and the normal MTU size is 1500, So does it means that while configuring the MPLS network on the Switches attached with the MPLS CE router we MUST have to configure the MTU size to 1520 or not.
Please confirm

MPLS is not configured between the CE and the PE. So if your IP mtu is 1500 then the switch between the CE and PE needs to support 1500 only.
The mpls mtu needs to be configured in the core where ethernet switches are used.
Hope this helps,

Frame Relay and MPLS

Hi,
I want to ask about the frame relay and MPLS.
Frame Relay Scenerio
The frames reached at the frame relay network and forwarded on the basis of DLCI. All the VCs are defined prior to the traffic on the network on the basis of DLCI (This is just like the MPLS network as packets are forwarded on the basis of Labels).
Now my Question is How can MPLS is used in frame relay network or what are its affects in the presence of DLCI (As DLCIs are also performing the same task and also works on layer 2) or these two are different equivalent technologies ?

Hi Muhammad,
The answer is : MPLS is working on FR like it's working on ethernet. Because the FR and Ethernet are running on Layer2. It's told that MPLS is working at layer 2.5 , meaning that is between Layer 3 , and Layer 2. So in order to work it needs a layer2 forwarding in your case FR's DLCI. On top of the Layer 2 it is the MPLS header.
Dan

IPX and MPLS

I am begining to implement an MPLS network. I have several sites that are using Novell 4.1 servers that are using IPX. At present I am using EIGRP and Frame Relay with some Point to Point connections. When I move all of these sites over to the MPLS network, what am I going to have to do to keep the IPX working between these servers.
Will IPX run on MPLS? Or will MPLS encapsulate the IPX Packet in IP?
Some of these servers cannot be upgraded to the Novell 5.0 or 5.1 using IP.

It's kind of funny the "MP" in MPLS still needs some time. I doubt we will see anything for carrying IPX natively inside MPLS, mainly because the demand isn't there in the service provider space.
There are emerging standards for bridging layer 2 inside MPLS - particularly VPLS. That may be an option, but it's not clear what platforms are supporting it right now as the standard is still in draft.
For the short-term, certainly upgrading to nate IP is most desirable. If that's not feasable, then GRE tunnels will work well with a small number of servers.
(Tunnels are point-to-point = n-squared)

Applications fail when "mpls mtu 1526" is configured

Hi,
I'm facing an issue with an MPLS VPN backbone.
A customer's IP host at one location can ping and traceroute to application servers at it's central site at another location. The IP path traverses four P/PE routers, as follows:
IP Host (spoke site) -- CE1 -- P/PE1 -- P/PE2 -- P/PE3 -- P/PE4 -- CE2 -- Servers (central site)
However, access to all applications fails.
Network configurations as follows:
(1) All the P/PE routers are Cisco 7609, SUP720-3BXL, IOS 12.2(18)SXF6.
(2) All the core links are configured with "mpls mtu 1526".
(3) All the core links are GE, connected to SPA-2X1GE on a 7600-SIP-400 linecard. Some connect to the SFP port on the SUP720.
(4) Only some of the P/PE routers are configured with "ip tcp path-mtu-discovery".
After removing the command "mpls mtu 1526" from all core links, access to all applications and services works again.
Please advise if I've configured anything wrongly.
Thank you.
B.Rgds,
Lim TS

There are two ways to look at this,
1) First To solve the problem, on all your Core and Core Facings links configure "mtu 1526 or larger" (PE-P, P-P) mtu 1526 or larger.
2) Second "MPLS MTU 1526" command only helps in labelling the fragmented payload which is beyond 1526. Till then if anything is fragmented it doesnt label the fragments.
So now why does it work when its removed,
a) verify what is your actual link mtu.
b) "mpls mtu" command doesnt change the physical mtu it just tells the IOS when to label fragments. and the 1526 is the threshold to fragment the labelled packet and label the fragments also.
c) One important thing to note is even when you dont configure the "mpls mtu" command it is still there by default but now it uses the MTU value of the physical link, so if your link is of 1500 MTU the default "mpls mtu" is also 1500.!
d) also go through this previous thread for more information the same topic has been discussed at length.
MPLS: MTU Ethernet MPLS Network Sep 26, 2006
HTH-Cheers,
Swaroop.

Why we need mpls mtu command?

if interface mtu is not big enough to take mpls packet. we just increase interface mtu. why we need mpls mtu command.
if we just only increase mpls mtu.there is problem if mpls mtu biger than interface mtu. so it seem mpls mtu command is useless.
why we need mpls mtu command!
thank you!
Jun

Hi,
i test it in netowork,like this\
topology is simple
7609-1pe--sip GE spa----7609-2p--pos---7609-3p--flexwan E1-----7604-1pe--ge--ce
i config mpls mtu 1524 between 7609-1 and 7609-2 . and keep interface mtu 1500 default.
ping packet from 7609-1 to 7604-1 loopback 0.
ping 1500 byte packet is ok, but ping 1501 byte packet is totally lost.then i config mtu 1524 between 7604-1pe and 7609-3, it is useless,not work, i can't see packet coming from 7609-1 on 7604-1.
then i add config mtu 1524 between 7609-1pe and 7609-2. config mtu 1500 between 7604-1 and 7609-3,ping 1501 bytes from 7609-1 to 7604-1 loopback0 is ok. but i can see fragment from show ip traffic command in 7609-3.
i have a question, why we need mpls mtu command. if we don't change interface mtu,just only config mpls mtu 1524, it doesn't work, if we just change mpls mtu,how it work in the ios. if we config interface mtu 1524,interface mtu size is big enough, it seems mpls mtu command is useless, we don't need mpls mtu command, just increase interface mtu 1524 is ok.
why we need mpls mtu command. we just only change interface mtu is enough.
when i config mpls mtu override 1524,this is a warning in ios:
Setting the mpls mtu to 1524 on interface serial1/0/0:0, which is higher than the interface MTU
1500. This could lead to packet forwarding problems including packet drops.
You must set the MPLS MTU values equal to or lower than the interface MTU values.
thank you!
jun

MPLS MTU

We are facing serious problems related to MPLS MTU. Due to fragmentation some of the applications are not working. I have enabled the mpls mtu 1508 across the path of MPLS but some of our switches do not support jumbo frames.
The strange this is that we are not only facing this issue with customer which are connected with us via Ethernet (wireless and cable) but also customers having WAN connection like ATM.

Hi Ahmede...
We had a similar issue with Windows 2000/2003 platforms. In our case, it was a Microsoft bug which a patch fix it... However, we don't manage the Microsoft servers, so we decided to pursue this with a solution in the router. Fragmentation was the main cause, and fixed the problem by adding the following command to the interfaces :
ip tcp adjust-mss 1272
We are still working to identify why '1272', but if you ping from some PCs you can have a payload of up to 1400+, but from other workstations (mine is an XP) I could do only 1272. Hope this helps.

MPLS MTU on various ethernet controllers

Is there some documentation available which router ethernet interface controller supports which maximum frame size ?
Background:
We have some intra-PoP crossover FE connections in an MPLS VPN based network. To avoid fragmentation we'd like to increase the mpls mtu to e.g. 1520bytes. I know that this isn't an issue on a PA-2FE-TX (7206-VXR), but there are also c3745 used as PE / P boxes. Does anybody know what frame sizes the onboard FEs of the 3745 and the NMs of these platforms (e.g. NM-2FE2W) can support ?
There is a document available for switches on CCO:
http://www.cisco.com/warp/public/473/148.html
Something in that style whould be great ...
thanks,
Stefan

Any update on this ?

Layer 3 Etherchannel and MPLS MTU

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