[c-nsp] TCP Throughput / MTU problem ? with Cisco 7304 andMPLS VPN's
Eric Kagan
ekagan at axsne.com
Fri Jan 11 10:42:14 EST 2008
> It will be easier to look into this issue if you can provide
> the detail like
> where this router sits exactly. Like between P--P, PE--P,
> PE--PE. I believe
It's strictly a P router, the setup is 3 POP's on a fiber ring, 2 P
routers at each side for each fiber entrance. P's are connected on Gig
backbone to PE routers
POP1
P-P
/ \
P P P P
O | | O
P P-----P P
2 3
> that if packets are passing out from this interface and being
> labeled on the
> device very first time you need to set ip mtu too. In Cisco
> mpls mtu command
> only work for labeled packets.
One thing I did forget to mention. The 7206 has physical interface MTU
= 1500, MPLS MTU 1546 and works fine on over 20 routers. Its just the
one 7304 that is having an issue. Currently, I have not changed
physical interface MTU on 7304, its 1500. I have tried MPLS MTU 1546
(and yes I got the error msg setting MTU above physical can cause
problems....) and MPLS MTU 1520
7304:
> interface GigabitEthernet1
> mpls mtu 1520
> mpls label protocol ldp
> mpls ip
GigabitEthernet1 is up, line protocol is up
Hardware is BCM1250 Internal MAC, address is 001c.5881.7001 (bia
001c.5881.7001)
MTU 1500 bytes, BW 1000000 Kbit, DLY 100000 usec,
reliability 255/255, txload 1/255, rxload 1/255
7206: (Working fine along this path)
interface GigabitEthernet0/2
mpls label protocol ldp
tag-switching mtu 1546
tag-switching ip
!
ma.wstr2.core1#show int g0/2
GigabitEthernet0/2 is up, line protocol is up
Hardware is BCM1250 Internal MAC, address is 0018.1819.851a (bia
0018.1819.851a)
MTU 1500 bytes, BW 50 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Full-duplex, 1000Mb/s, link type is autonegotiation, media type is SX
>
> Second if there are some gre tunnels involved along with mpls
> thn you may
> need to further tweak mtu settings.
There are currently no GRE tunnels
>
> Regards,
> Masood Ahmad Shah
>
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Eric Kagan
> Sent: Friday, January 11, 2008 7:51 PM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] TCP Throughput / MTU problem ? with Cisco
> 7304 and MPLS
> VPN's
>
> I am running in to a strange problem and hopfeully someone
> here can help. I
> did open a Cisco TAC case but I don't think they understand
> the issue or
> maybe I didn't explain it well.
>
> We have MPLS enabled through the core of our network for customer MPLS
> VPN's. Until now, all devices have been 7206VXR's w/
> NPE-G1's and we are
> only using the 3 internal Gig ports on the Processor. I
> upgraded one of the
> VXR's to a 7304 and configured it the same as the 7206. The
> router itself
> is working fine, BGP is working, regular IP traffic /
> throughout is fine
> (iperf tests have no issues). I have confirmed interface
> MTU's, switch
> MTU's and everything is configured the same as before. When
> VPN traffic
> goes through this link, I get reports of TCP requests
> starting and then
> stopping (i.e. SSH makes connection but can't pass data, or
> do an 'ls', etc
> or HTTP Get seems to connect but doesn't pass data back). It
> all sounds
> very similar to MTU issues I experienced and read about on
> MPLS interfaces.
> If I reroute the traffic around the ring away from the 7304
> everything works
> fine again - and the problem connections are resolved in seconds. I
> originally had the MTU set to 1546 on the 7304 (I used to use
> 1524 but some
> of the L2 VPN's needed more so I bumped them up). I came across the
> document MPLS MTU Command Changes
> (http://www.cisco.com/en/US/products/ps6566/products_feature_g
> uide09186a0080
> 629db0.html) which I found interesting so I set the MPLS MTU
> to 1520 with no
> avail. Below is show ver and config clips along with a few
> show commands.
> I am hoping someone has seen this and knows how to resolve.
>
> Thanks
> Eric
>
>
>
>
>
> Cisco IOS Software, 7300 Software (C7300-K91P-M), Version 12.2(31)SB6,
> RELEASE SOFTWARE (fc1)
> System image file is "disk0:c7300-k91p-mz.122-31.SB6.bin"
> cisco 7300 (NPEG100) processor (revision B) with
> 983040K/65536K bytes of
> memory.
>
>
> mpls label protocol ldp
> !
> interface Loopback0
> ip address 10.11.12.214 255.255.255.255
> !
> interface GigabitEthernet0
> desc Backbone Switch
> ip address 10.11.13..1 255.255.255.224
> ip flow ingress
> load-interval 30
> media-type rj45
> speed auto
> duplex auto
> negotiation auto
> mpls mtu 1520
> mpls label protocol ldp
> mpls ip
> !
> interface GigabitEthernet1
> description Fiber to POP1
> ip address 10.11.14.26 255.255.255.252
> ip flow ingress
> load-interval 30
> delay 10000
> media-type gbic
> speed auto
> duplex auto
> negotiation auto
> mpls mtu 1520
> mpls label protocol ldp
> mpls ip
> !
> interface GigabitEthernet2
> description Backbone Failover
> bandwidth 50
> ip address 10.11.14.253 255.255.255.248
> ip flow ingress
> load-interval 30
> media-type rj45
> speed auto
> duplex auto
> negotiation auto
> mpls mtu 1520
> mpls label protocol ldp
> mpls ip
> !
> router bgp xxxxx
> no synchronization
> bgp log-neighbor-changes
> neighbor RR_SERVER peer-group
> neighbor RR_SERVER remote-as xxxxx
> neighbor RR_SERVER update-source Loopback0
> neighbor RR_SERVER next-hop-self
> neighbor RR_SERVER send-community both
> neighbor 10.11.12.201 peer-group RR_SERVER
> neighbor 10.11.12.201 description pecore-mma
> neighbor 10.11.12.203 peer-group RR_SERVER
> neighbor 10.11.12.203 description pecore-wma
> no auto-summary
> !
>
> #show mpls int
> Interface IP Tunnel BGP Static Operational
> GigabitEthernet0 Yes (ldp) No No No Yes
> GigabitEthernet1 Yes (ldp) No No No Yes
> GigabitEthernet2 Yes (ldp) No No No Yes
>
>
>
>
> #show mpls ldp disc
> Local LDP Identifier:
> 10.11.12.214:0
> Discovery Sources:
> Interfaces:
> GigabitEthernet0 (ldp): xmit/recv
> LDP Id: 10.11.12.216:0
> LDP Id: 10.11.12.215:0
> LDP Id: 10.11.12.217:0
> GigabitEthernet1 (ldp): xmit/recv
> LDP Id: 10.11.12.203:0
> GigabitEthernet2 (ldp): xmit/recv
> LDP Id: 10.11.12.215:0
> LDP Id: 10.11.12.217:0
> LDP Id: 10.11.12.216:0
>
>
> Also, show mpls ldp binding and show mpls ldp nei show all
> the proper info.
> I sent an update back to Cisco on the TAC case but think
> someone here may
> understand and help quicker. Any help or insight would be appreciated.
>
> Thanks
> Eric
>
>
>
>
> Eric Kagan
>
>
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