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Cisco 7246vxr mtu problem

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spacecowboy
Cisco 7246vxr mtu problem

Trying to configure all-in-one cmts. Everything works, but cable modems can't fully load webpages. It is acting like an MTU problem, but I've thrown every MTU setting at it and still pages load slow. I don't know if it is an MTU problem or a cable card config problem. Levels look good on cable plant. Modems come up connect via PPPoE very fast.

Pings work like a champ (by name or IP) without dropping any packets. Using PPPoE via switch port to this 7246vxr and browsing the web works like a champ too. Going through the cable interface creates the problem. I've tried both cards- same result, halfway loading pages.

Any help would be appreciated. This is first time setting up a 7246 as a CMTS going from an old nortel cmts.....config below

version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
!
hostname xxx
!
boot-start-marker
boot system flash disk2:ubr7200-ik9su2-mz.123-17a.BC.bin
boot-end-marker
!
logging buffered 16384 debugging
!
clock timezone xxx
clock summer-time xxx recurring
no cable qos permission create
no cable qos permission update
cable qos permission modems
cable time-server
!
cable config-file standard.cm
service-class 1 max-upstream 1000
service-class 1 guaranteed-upstream 256
service-class 1 max-downstream 3000
service-class 1 max-burst 500
cpe max 5
timestamp
!
aaa new-model
!
!
aaa authentication login xxx local line
aaa authentication ppp default group radius
aaa authorization exec default local
aaa authorization network default group radius
aaa accounting delay-start
aaa accounting update newinfo
aaa accounting network default start-stop group radius
aaa session-id common
ip subnet-zero
!
!
ip cef
ip domain name xxxxxxx
ip name-server xxxxxxx
ip name-server xxxxxxx
!
ip dhcp pool modem-pool
network 10.10.10.0 255.255.255.0
bootfile standard.cm
next-server 10.10.10.1
default-router 10.10.10.1
option 66 ip 10.10.10.1
option 7 ip 10.10.10.1
option 4 ip 10.10.10.1
option 2 hex ffff.8f80
lease 3 0 10
!
vpdn enable
!
vpdn-group cablemodem
accept-dialin
protocol pppoe
virtual-template 1
pppoe limit per-mac 1
pppoe limit per-vlan 250
!
!
!
!
!
buffers small permanent 1024
buffers small max-free 1024
buffers small initial 1024
!
!
interface Loopback0
no ip address
!
interface GigabitEthernet0/1
ip address xxx.xxx.xxx.2 xxx.xxx.xxx.0
no ip redirects
no ip unreachables
no ip proxy-arp
ip tcp adjust-mss 1452
duplex auto
speed auto
media-type rj45
no negotiation auto
arp timeout 300
!
interface GigabitEthernet0/1.17
description to Cable modems NEW
encapsulation dot1Q 17
no ip redirects
no ip proxy-arp
pppoe enable
no snmp trap link-status
arp timeout 300
!
interface GigabitEthernet0/2
ip address 10.10.11.4 255.255.255.0
shutdown
duplex auto
speed auto
media-type rj45
no negotiation auto
!
interface GigabitEthernet0/3
no ip address
shutdown
duplex auto
speed auto
media-type rj45
no negotiation auto
!
interface Cable3/0
no ip address
cable tftp-enforce
no cable packet-cache
cable bundle 1
cable downstream annex B
cable downstream modulation 256qam
cable downstream interleave-depth 32
cable downstream frequency 117000000
cable downstream channel-id 0
cable upstream 0 frequency 26752000
cable upstream 0 channel-width 3200000
cable upstream 0 minislot-size 2
cable upstream 0 power-level 0
cable upstream 0 modulation-profile 1
no cable upstream 0 shutdown
cable upstream 1 frequency 26752000
cable upstream 1 channel-width 3200000
cable upstream 1 minislot-size 2
cable upstream 1 power-level 0
cable upstream 1 modulation-profile 1
no cable upstream 1 shutdown
cable upstream 2 frequency 26752000
cable upstream 2 channel-width 3200000
cable upstream 2 minislot-size 2
cable upstream 2 power-level 0
cable upstream 2 modulation-profile 1
no cable upstream 2 shutdown
cable upstream 3 frequency 26752000
cable upstream 3 channel-width 3200000
cable upstream 3 minislot-size 2
cable upstream 3 power-level 0
cable upstream 3 modulation-profile 1
no cable upstream 3 shutdown
cable upstream 4 frequency 26752000
cable upstream 4 channel-width 3200000
cable upstream 4 minislot-size 2
cable upstream 4 power-level 0
cable upstream 4 modulation-profile 1
no cable upstream 4 shutdown
cable upstream 5 frequency 26752000
cable upstream 5 channel-width 3200000
cable upstream 5 minislot-size 2
cable upstream 5 power-level 0
cable upstream 5 modulation-profile 1
no cable upstream 5 shutdown
pppoe enable
no keepalive
!
interface Cable4/0
no ip address
load-interval 30
shutdown
no cable packet-cache
cable default-phy-burst 4000
cable bundle 1
cable downstream annex B
cable downstream modulation 256qam
cable downstream interleave-depth 32
cable downstream frequency 117000000
cable downstream channel-id 0
cable upstream 0 frequency 26752000
cable upstream 0 channel-width 3200000
cable upstream 0 minislot-size 2
cable upstream 0 power-level 0
cable upstream 0 modulation-profile 1
no cable upstream 0 shutdown
cable upstream 1 frequency 26752000
cable upstream 1 channel-width 3200000
cable upstream 1 minislot-size 2
cable upstream 1 power-level 0
cable upstream 1 modulation-profile 1
no cable upstream 1 shutdown
cable upstream 2 frequency 26752000
cable upstream 2 channel-width 3200000
cable upstream 2 minislot-size 2
cable upstream 2 power-level 0
cable upstream 2 modulation-profile 1
no cable upstream 2 shutdown
cable upstream 3 channel-width 1600000
cable upstream 3 minislot-size 4
cable upstream 3 modulation-profile 1
cable upstream 3 shutdown
cable upstream 4 channel-width 1600000
cable upstream 4 minislot-size 4
cable upstream 4 modulation-profile 1
cable upstream 4 shutdown
cable upstream 5 channel-width 1600000
cable upstream 5 minislot-size 4
cable upstream 5 modulation-profile 1
cable upstream 5 shutdown
pppoe enable
no keepalive
!
interface Virtual-Template1
mtu 1492
ip unnumbered GigabitEthernet0/1
ip verify unicast reverse-path
no ip redirects
no ip unreachables
no ip proxy-arp
no logging event link-status
peer default ip address pool cablemodem
keepalive 60 10
ppp authentication pap chap
!
interface Bundle1
ip address 10.10.10.1 255.255.255.0
no cable arp filter request-send
no cable arp filter reply-accept
!
ip local pool cablemodem xxx.xxx.xxx.1 xxx.xxx.xxx.254
ip classless
ip route 0.0.0.0 0.0.0.0 xxx.xx.xx.x
no ip http server
no ip http secure-server
!
!
ip radius source-interface GigabitEthernet0/1

!
snmp-server community xxxxxxxx RO
snmp-server enable traps tty
!
radius-server host xxx.xxx.xxx.xxx auth-port xxxx acct-port xxxx
radius-server key x xxxxxxxxxxxx

mbowe
I've never done PPPoE on a

I've never done PPPoE on a CMTS before, but this is pretty common on ADSL. A trick we use there is to add "ip tcp adjust-mss 1452" to the virtual-template. Perhaps give that a try on the CMTS, hopefully your IOS supports it!

Also on the template, I think it should be "ip mtu 1492" not "mtu 1492"

mbowe
Oh I see you already have the

Oh I see you already have the adjust-mss on the gig0/1

Should work OK there I suppose, but perhaps try it on the template instead

spacecowboy
works now

Thanks for the help!

Yesterday I went and narrowed it down to I couldn't ping with a 437 byte package but could with 436. I disabled pppoe and as expected I could ping with 444 bytes but not 445.

So I disabled all MTU settings on the Virtual-Template. Now I could ping with 1436 bytes but not 1437. I changed the ip tcp adjust-mss to 1428 on Gig0/1 and everything works. Pages load normally, speed tests work great- tested all the way up to 30Mbps down on a cable modem.

Not sure about why I could only ping with 436 bytes with that config......I'm still trying to figure that out.

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