q DNS multihomes

q DNS multihomes

Post by Jaso » Tue, 06 May 2003 17:37:01


Now my linux box DNS has 2 NICs.  Could the DNS be the external and internal
at the same time?
The IP eth0 is 139.175.a.b which is public, whrere eth1 is
For example,

                                100     ; Serial
                                300             ; Refresh - 5 Minutes
                                60              ; Retry - 1 minute
                                1209600         ; Expire - 2 Weeks
                                43200)          ; Minimum - 12 Hours
                                IN      NS      ns.mydomain.com.
                                IN      A       139.175.a.b
   zzz                        IN      A

Where the machine zzz.mydomain.com is another server in my domain.
What would be the consequence?
Any help will be appreciated.



q DNS multihomes

Post by Barry Margoli » Wed, 07 May 2003 00:05:25

>Now my linux box DNS has 2 NICs.  Could the DNS be the external and internal
>at the same time?

Yes.  See the "views" facility in BIND, which allows you to configure a
single server to present different versions of the domains depending on the
address of the client.


Genuity Managed Services, a Level(3) Company, Woburn, MA
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.


1. BGP multihoming with uneven links - sample config and Qs

Hi, everyone,

I was hoping for some input from some of the BGP gurus here, in regards
to a suggested configuration of a dual ISP + 1 router, with uneven links
(DS3 and T1). I have asked earlier about this, and I have been advised to
upgrade the T1 to DS3, but we do not have that financial capability, and
would rather eliminate some Internet services, if the DS3 goes down ...
but this is just logistics. The issue I would like to raise is a
configuration suggested to us by the ISP with the T1 (I'll call them
ISP-T1), involving something along these lines:

router bgp <my-ASN>
no synchronization
no bgp log-neighbor-changes
bgp dampening
network <my-public-net-class-C> --> this one comes from the ISP-T1
neighbor ISP-T1 peer-group
neighbor ISP-T1 remote-as XXXX --> ISP-T1 AS number
neighbor ISP-T1 version 4
neighbor ISP-T1 send-community
neighbor ISP-DS3 peer-group
neighbor ISP-DS3 remote-as YYYY --> ISP-T1 AS number
neighbor ISP-DS3 version 4
neighbor ISP-DS3 route-map localpref in
neighbor ISP-DS3 route-map ISP-DS3 out
no auto-summary

.... various ip route ...

ip bgp-community new-format
ip as-path access-list 10 deny _XXXX_
ip as-path access-list 10 permit .*
ip as-path access-list 20 deny _YYYY_
ip as-path access-list 20 permit .*
ip flow-export version 5
ip flow-export destination <my-flow-collector>

.... other access lists ...

route-map ISP-T1 permit 10
        match as-path 10
        set community ZZZZ:WW
route-map localpref permit 10
        set local preference 300
route-map ISP-DS3 permit 10
        match as-path 20


So - looking at the above: ISP-T1 implies that he could help us control
the majority of the traffic through ISP-DS3, because of a community
ZZZZ:WW used at his end, also, and the local preference. My questions are:
1. I do not understand (yet) all this, so I have no idea what the
community woullld do (how does it get defined at the ISP end, top allow -
presumably - more routes to come the other way (through ISP-DS3)?
2. What would happen in case of ISP-T1 failure (under two scenarios: my
link to them, or their end)?

NOTE: all of the above has been typed just now, as we scribbled the stuff
over the phone, on a notepad, so if there are typos, please do not
consider them fundamental mistakes.

I would appreciate any comments,

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