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New Member

how to set IOS as DNS server forwarding to servers set by ip address dhcp ?

int FastEthernet0/0

description inside

ip address i.i.i.i m.m.m.m

int FastEthernet0/1

description outside1 to ISP#1 with DNS0 o.o.o.1 and DNS1 o.o.o.2

ip address dhcp

int FastEthernet0/2

description outside2 to ISP#2 with DNS0 o.o.o.3 and DNS1 o.o.o.4

ip address dhcp

... sla configured so if outside1 goes down outside2 is selected

... now what I want to do is to set this router to act as a DNS server on i.i.i.i (as stated on inside):

ip dns server ... this server should respond to local hosts such as:

ip domain name whatever.com

ip host computer1 x.x.x.x

ip host computer2 x.x.x.x

ip host computer3 x.x.x.x

... and this server should forward unknown hosts to the DNS servers stated on the current outside connection

if outside1 is active local DNS server should forward to o.o.o.1 o.o.o.2

if outside2 is active local DNS server should forward to o.o.o.3 o.o.o.4

while my internal DNS server will always point to i.i.i.i knowing nothing about which ISP is active at any given moment

... so; how do I set the DNS forwarders to the ones assigned by the active dhcp lease ?

why this ?

because I can place just one forwarder (i.i.i.i) on my internal AD DNS server and forget about what ISP I'm connected at any moment, otherwise I have to manually change the DNS list on my Windows box everytime I switch over to the other ISP with its associated DNS servers

eg:

sh dhcp server

DHCP server: ANY (255.255.255.255)

Leases: 2

Offers: 1 Requests: 1 Acks : 2 Naks: 0

Declines: 0 Releases: 0 Query: 0 Bad: 0

DNS0: o.o.o.1, DNS1: o.o.o.2

Subnet: 255.255.255.0

sh dhcp lease

Temp IP addr: 192.168.1.101 for peer on Interface: ...

Temp sub net mask: 255.255.255.0

DHCP Lease server: 192.168.1.1, state: 5 Bound

DHCP transaction id: 1D81

Lease: 741 secs, Renewal: 370 secs, Rebind: 648 secs

Temp default-gateway addr: 192.168.1.1

Next timer fires after: 00:05:46

Retry count: 0 Client-ID: ...

Client-ID hex dump: ...

Hostname: ...

Temp IP addr: 0.0.0.0 for peer on Interface: ...

Temp sub net mask: 0.0.0.0

DHCP Lease server: 0.0.0.0, state: 11 Purging

DHCP transaction id: 1D82

Lease: 0 secs, Renewal: 0 secs, Rebind: 0 secs

Next timer fires after: 00:00:30

Retry count: 0 Client-ID: ...

Client-ID hex dump: ...

Hostname: ...

I want something set like [ip dns forwarder o.o.o.1 o.o.o.2] so nslookup site.com i.i.i.i should return the appropriate address using my router

can somebody point me in the right direction ?

1 REPLY
New Member

Re: how to set IOS as DNS server forwarding to servers set by ip

... self-solved but not sure if it's the right/optimal way:

ip dns view default

no domain lookup

no dns forwarding

ip dns view dnsVedge

domain name whatever.com

domain name-server interface FastEthernet0/1

domain resolver source-interface FastEthernet0/0

domain round-robin

ip dns view-list dnsVLedge

view dnsVedge 1

ip dns server view-group dnsVLedge

ip dns server

... default view not used; using dnsVedge instead:

sh ip dns view

DNS View dnsVedge parameters:

Logging is off

DNS Resolver settings:

Domain lookup is enabled

Default domain name: whatever.com

Domain search list:

Lookup timeout: 3 seconds

Lookup retries: 2

Domain name-servers:

o.o.o.1

o.o.o.2

Resolver source interface: FastEthernet0/0/0

Round-robin'ing of IP addresses is enabled

DNS Server settings:

Forwarding of queries is enabled

Forwarder addresses:

DNS View default parameters:

Logging is off

DNS Resolver settings:

Domain lookup is disabled

Default domain name: whatever.com

Domain search list:

Lookup timeout: 3 seconds

Lookup retries: 2

Domain name-servers:

o.o.o.1

o.o.o.2

DNS Server settings:

Forwarding of queries is disabled

Forwarder addresses:

... right now it's working fine with both ISPs

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