INTELLIGENT WORK FORUMS
FOR COMPUTER PROFESSIONALS

Log In

Come Join Us!

Are you a
Computer / IT professional?
Join Tek-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Tek-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Possible DNS problem using Cisco 877

Possible DNS problem using Cisco 877

(OP)
I have managed to get my Cisco 877 to connect to the internet, authenticate etc. All my devices can connect wirelessly and obtain IP addresses; the NATs that are plugged in to the router are able to be accessed by my laptop, so internal network appears to be working; BUT ... whilst I can "ping" ip addresses from a command line on my laptop, use of the domain name returns an error that the domain cannot be located.

My laptop can also not access any web pages. My mobile phone, also connecting wirelessly to the 877, however, CAN - it can acess web pages, download email - everything.

I have added name-servers to my global config, dns-servers to my DHCP pool, added "import all" to the DHCP pool, set MTU 1492 in the Dialer interface and adjust-mss to 1452 in the Bridge Group interface BVI1; I have also set ppp tcp ipcp dns request and wins request in the Dialer interface.

From the laptop, if I ping google.com, it fails, telling me it cannot find the named host. If I do an nslookup though, I get the following output:

C:\Windows\System32>nslookup google.com
Server: resolver1.opendns.com
Address: 208.67.222.222

Non-authoritative answer:
Name: google.com
Addresses: 2404:6800:4006:807::200e
172.217.25.174

So nslookup works..... but I still can't ping, or connect to the web...

a show ip int on the Cisco reveals the following nuggets:
Dialer 0 has MTU - 1492
NVI 0 has MTU - 1514
BVI 1 has MTU - 1500 ( with ip tcp adjust-mss 1452 set in interface BVI1)

I tried changing adjust-mss in BVI 1 to the maximum 1460 and MTU in Dialer 0 to 1500. No, same problem.

The last two outputs may mean something - I truly don't know for I lack the knowledge or experience to interpret them, but I did a show ip cef from the Router:

Cisco877#show ip cef
Prefix Next Hop Interface
0.0.0.0/0 attached Dialer0
0.0.0.0/32 receive
144.138.131.0/24 attached Dialer0
144.138.131.0/32 receive
144.138.131.214/32 receive
144.138.131.255/32 receive
155.143.128.142/32 attached Dialer0
192.168.0.0/24 attached BVI1
192.168.0.0/32 receive
192.168.0.1/32 receive
192.168.0.2/32 192.168.0.2 BVI1
192.168.0.3/32 192.168.0.3 BVI1
192.168.0.16/32 192.168.0.16 BVI1
192.168.0.17/32 192.168.0.17 BVI1
192.168.0.20/32 192.168.0.20 BVI1
192.168.0.255/32 receive
224.0.0.0/4 drop
224.0.0.0/24 receive
255.255.255.255/32 receive

And then a show ip dns statistics :

Cisco877#show ip dns statistics
DNS requests received = 25 ( 24 + 1 )
DNS requests dropped = 0 ( 0 + 0 )
DNS responses replied = 0 ( 0 + 0 )

Forwarder queue statistics:
Current size = 0
Maximum size = 6
Drops = 0

Director queue statistics:
Current size = 0
Maximum size = 0
Drops = 0

So .... does any of this mean anything to anyone......?

RE: Possible DNS problem using Cisco 877

(OP)
I'll answer this one as well, for anyone reading ... The issue seemed to be an MTU mismatch. adding the lines "ip nat enable" to bothe Dialer0 and BVI1 also helped!!
The MTU mismatch was stabilised by setting MTU in Dialer0 to 1460 and adding "ppp tcp adjust-mss 1420" to both Dialer0 and BVI1

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Tek-Tips Forums free from inappropriate posts.
The Tek-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Tek-Tips forums is a member-only feature.

Click Here to join Tek-Tips and talk with other members!

Resources

Close Box

Join Tek-Tips® Today!

Join your peers on the Internet's largest technical computer professional community.
It's easy to join and it's free.

Here's Why Members Love Tek-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close