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Routing issue c1841 and bridged modem

toneydial
Level 1
Level 1

Hi all,

 

I'm looking for help resolving a routing issue when making a configuration change to a working router.   Currently the router works well using an ADSL HWIC, with the LAN on fa0/1 and no connection to fa0/0.

 

To take advantage of a faster connection, I'm attempting to use an external bridged modem on fa0/0, with the intent to upgrade to VDSL service.   Ideally, the C1841 will continue to perform NAT and hold the PPPoE credentials.

 

When using the external modem, the ATM interfaces are placed in shutdown, and fa0/0 is placed in service.  I'm able to authenticate PPPoE as usual, but unable to route via browser either by DNS lookup or entered IP.   I can ping from a PC, but NSLOOKUP fails multiple DNS servers and tracert dies at the 1841 router.    I tried using an extended named ACL with no change.    

 

NAME: "chassis", DESCR: "1841 chassis"

PID: CISCO1841         , VID: V05 , SN:

 

NAME: "WIC 1", DESCR: "ADSL over POTS"

PID: HWIC-1ADSL        , VID: V01 , SN:

 

 

Router#sh flash

-#- --length-- -----date/time------ path

1     25645308 Jan 12 2019 01:57:10 c1841-broadband-mz.124-24.T3.bin

 

Current configuration : 2629 bytes

!

version 12.4

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname Router

!

boot-start-marker

boot-end-marker

!

logging message-counter syslog

enable secret 5 xxxxxxxxxxxxxxxxxxxx

!

no aaa new-model

clock timezone CST -6

ip source-route

!

!

!

!

ip cef

ip name-server 208.67.220.220

ip name-server 208.67.222.222

multilink bundle-name authenticated

vpdn enable

!

vpdn-group 1

 request-dialin

  protocol pppoe

!

!

!

vtp mode transparent

username xxxx secret 5 xxxxxxxxxxxxxxxxxx

archive

 log config

  hidekeys

!

!

!

!

!

interface FastEthernet0/0

 description WAN

 no ip address

 no ip redirects

 no ip unreachables

 no ip proxy-arp

 shutdown

 duplex auto

 speed auto

 pppoe enable

 pppoe-client dial-pool-number 1

 no cdp enable

!

interface FastEthernet0/1

 description LAN

 no ip address

 ip tcp adjust-mss 1452

 duplex auto

 speed auto

!

interface FastEthernet0/1.10

 description Management

 encapsulation dot1Q 10

 ip address 10.1.10.1 255.255.255.0

!

interface FastEthernet0/1.20

 description Wireless

 encapsulation dot1Q 20

 ip address 10.1.20.1 255.255.255.0

 ip nat inside

 no ip virtual-reassembly

 ip tcp adjust-mss 1452

!

interface FastEthernet0/1.100

 description 1st Floor

 encapsulation dot1Q 100

 ip address 10.1.100.1 255.255.255.0

 ip nat inside

 no ip virtual-reassembly

 ip tcp adjust-mss 1452

!

interface FastEthernet0/1.200

 description 2nd Floor

 encapsulation dot1Q 200

 ip address 10.1.200.1 255.255.255.0

 ip nat inside

 no ip virtual-reassembly

 ip tcp adjust-mss 1452

!

interface ATM0/1/0

 description ADSL WIC

 no ip address

 no atm ilmi-keepalive

 bundle-enable

 hold-queue 224 in

!

interface ATM0/1/0.1 point-to-point

 description WIC ATM sub-interface

 pvc 0/35

  pppoe-client dial-pool-number 1

 !

!

interface Dialer1

 ip address negotiated

 ip mtu 1492

 ip nat outside

 no ip virtual-reassembly

 encapsulation ppp

 ip tcp adjust-mss 1452

 dialer pool 1

 dialer-group 1

 no cdp enable

 ppp authentication pap callin

 ppp pap sent-username xxxxxxx password 0 xxxxxxxxxx

 ppp ipcp dns request accept

 ppp ipcp route default

 ppp ipcp address accept

!

ip forward-protocol nd

!

!

no ip http server

ip nat inside source list 1 interface Dialer1 overload

ip nat inside source static tcp 10.1.20.251 25565 interface Dialer1 25565

!

logging history size 30

access-list 1 deny   10.1.10.0 0.0.0.255

access-list 1 permit any

dialer-list 1 protocol ip permit

!

!

control-plane

 

1 Accepted Solution

Accepted Solutions

toneydial
Level 1
Level 1

Thanks for the replies!

 

The issue has been identified as a change in the ISP's processes.     

 

Six months, or so, back, the ISP instituted a new process by which the PPPoE credentials are attached to the hardware address of the DSL modem in a back-end system.   This prevents the user from swapping equipment at free-will: when the credentials are used with a 'new' modem, URL requests are redirected to a 'walled-garden' where the user can enter information about their account to permit the use of the new modem with the credentials.    

 

The reason I was never redirected to the walled-garden page was the use of 3rd party DNS servers - if anything other than the ISP's DNS servers are used, the page hangs and eventually times out.    

 

I was able to test and verify the problem by using a laptop with the bridged modem and setting up a PPPoE connection on the laptop.  

 

It should be stated that my ISP discourages the use of 3rd party DNS servers, bridged-modems and non-ISP equipment - it would seem that these may have been a consideration when instituting this new process.

View solution in original post

3 Replies 3

Francesco Molino
VIP Alumni
VIP Alumni
Hi

Your atm and fa0/0 are part of the sand dialer interface. You can configure the fa0/0 to dialer 2 to make sure the atm stays up.

When switching to fa0/0, can you share the output of sh ip int brie | ex unas and sho ip route commands please?

Thanks
Francesco
PS: Please don't forget to rate and select as validated answer if this answered your question

Try configuring fa0/0 in dialer 2 and check if that works.

Please do not hesitate to click the STAR button if you are satisfied with my answer.

toneydial
Level 1
Level 1

Thanks for the replies!

 

The issue has been identified as a change in the ISP's processes.     

 

Six months, or so, back, the ISP instituted a new process by which the PPPoE credentials are attached to the hardware address of the DSL modem in a back-end system.   This prevents the user from swapping equipment at free-will: when the credentials are used with a 'new' modem, URL requests are redirected to a 'walled-garden' where the user can enter information about their account to permit the use of the new modem with the credentials.    

 

The reason I was never redirected to the walled-garden page was the use of 3rd party DNS servers - if anything other than the ISP's DNS servers are used, the page hangs and eventually times out.    

 

I was able to test and verify the problem by using a laptop with the bridged modem and setting up a PPPoE connection on the laptop.  

 

It should be stated that my ISP discourages the use of 3rd party DNS servers, bridged-modems and non-ISP equipment - it would seem that these may have been a consideration when instituting this new process.

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