06-13-2019 10:11 AM
We have about a dozen locations all using the same hardware and configuration (*mostly) except for their subnets. Each location has a T1 MPLS interface and a Local Broadband interface for Internet access. Since there's a few of our own websites which on the internal DNS server route to their local IP Addresses, in these remote offices we wanted them to route to their Public IP so they go through the local broadband instead of back over the T1 line. So we setup the ISR as a DNS server, and added a few "ip host <hostname> <public ipAddr>". So any DNS request not found on their ISR's local host table gets forwarded to our internal DNS server.
All the locations are working correctly except for one. The only difference with this one location is that their local Broadband won't allow me to set a static ip address on the interface going to the broadband modem. Instead, it's configured for DHCP. And with this, it appears they can't reach any internal hostname unless its explicitly configured on their ISR with an "ip host ..." command.
Also, since BGP handles all the internal routes back over the MPLS, there's a default route in each location pointing to the local broadband router's ip address. And in this one location, I had to use the following since it's DHCP, "ip route 0.0.0.0 0.0.0.0 dhcp".
Any idea why this is working this way? I assume its a product of the interface being DHCP. But, I don't know why?
Thanks in Advance,
06-13-2019 03:37 PM
Hi @Matthew Martin,
So you when using DHCP to get the WAN address, does the Router receive the DNS servers too?
06-14-2019 10:29 AM
06-14-2019 10:37 AM
show ip dns servers show ip dns view
06-14-2019 10:47 AM
Found this command to attempt to ignore the DNS server information received via DHCP on IOS
interface GigabitEthernetx/x ip address dhcp no ip dhcp client request dns-nameserver
Give it a try!
06-14-2019 11:28 AM
06-14-2019 11:30 AM
06-14-2019 12:28 PM
Most likely since the DHCP negotiation needs to happen once again.
06-14-2019 03:03 PM
06-14-2019 03:07 PM
It should work too.
06-18-2019 10:25 AM
So this past weekend I attempted this fix for the dhcp interface. But, it appears to still be showing the DNS servers coming through for that interface.
I added the following to the interface:
#show run int Gi0/0/0 Building configuration... Current configuration : 317 bytes ! interface GigabitEthernet0/0/0 description Broadband Internet Gateway no ip dhcp client request domain-name no ip dhcp client request dns-nameserver ip dhcp client client-id GigabitEthernet0/0/0 ip address dhcp ip nat outside zone-member security INTERNET media-type rj45 negotiation auto end
I then did a "release dhcp GigabitEthernet 0/0/0", then I did "renew dhcp GigabitEthernet 0/0/0". And after that I ran the "show ip dns servers" command, and it was still showing that interface's DNS servers that its getting via DHCP. So I then tried to do a "shut", then "no shut" on the interface. And after the interface came back up, I'm still seeing those DNS servers...
Any idea what could be going wrong here?
06-25-2019 12:12 PM
09-03-2020 02:28 AM
It seems like a bug.
My ISR1921 also has this problem, the "no ip dhcp client request ..." commands take no effect.
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