Re: DNS and Netview

[Ken Viola <kviola@cpcug.org>]

Todd,

The following is an excerpt from Cisco's public documentation and should help
understand the nature and usage of loopback:
(http://www.cisco.com/univercd/cc/td/doc/product/software/ios11/cbook/ciproute.htm#38888
and
http://www.cisco.com/univercd/cc/td/doc/cisintwk/intsolns/as5xipmo/sysmgt.htm
and
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/fun_r/frprt3/frd3001.htm#xtocid2988327)

Force the Router ID Choice with a Loopback Interface

OSPF uses the largest IP address configured on the router's interfaces as its
router ID. If the interface associated with this IP address is ever brought
down, or if the address is removed, the OSPF process must recalculate a new
router ID and resend all of its routing information out its interfaces.

If a loopback interface is configured with an IP address, the router will use
this IP address as its router ID, even if other interfaces have larger IP
addresses. Since loopback interfaces never go down, greater stability in the
routing table is achieved.

OSPF automatically prefers a loopback interface over any other kind, and it
chooses the highest IP address among all loopback interfaces in the router.
If no loopback interfaces are present, the highest IP address in the router
is chosen. You cannot tell OSPF to use any particular interface.

To configure an IP address on a loopback interface, perform the following
tasks, starting in global configuration mode:
  Task
Command
  Step 1 Create a loopback interface,                         interface
loopback 01
which places you in interface configuration mode.

  Step 2 Assign an IP address to this interface.           ip address address
mask2


  1This command is documented in the "Interface Commands" chapter of the
Router Products Command Reference publication.
  2This command is documented in the "IP Commands" chapter of the Router
Products Command Reference publication.

snmp-server trap-source Loopback0  - Enables traps for unsolicited
notifications for configuration changes, environmental variables, and device
conditions.


A sample (name and IP changed to protect the innocent) config follows:

This example is for a router named 'kwv001gate155.test.case.com'

---router configuration sample---
!
hostname kwv001gate155
!
interface Loopback0
ip address 179.118.125.6 255.255.255.252
snmp-server trap-source  Loopback0
!

The following example is provided for reference for updating DNS. I know you
didn't ask but it helps to describe my initial issue.

The forward entries would look like this:

kwv001gate155.test.case.com.    IN   A        179.118.125.6
                                                   IN   A        179.118.98.1

                                                   IN   A
179.118.98.65

(Note: the 2nd and 3rd ?A? records correspond to additional interfaces in the
router and are not necessary if using the loopback address)

The reverse lookup entries would look like this:

6.125.118.179.IN-ADDR.ARPA.      IN   PTR      kwv001gate155.test.case.com.
1.98.118.179.IN-ADDR.ARPA.        IN   PTR      kwv001gate155.test.case.com.
65.98.118.179.IN-ADDR.ARPA.      IN   PTR      kwv001gate155.test.case.com.

(Note: the 2nd and 3rd ?PTR? records correspond to additional interfaces in
the router and may not be necessary if using the loopback address)

Of course, it is also possible to create an alias or two for the router. The
aliases would be put in the forward lookup file and would look something like
this:

moe.test.case.com.              IN   CNAME    kwv001gate155.test.case.com.
larry.test.case.com.              IN   CNAME    kwv001gate155.test.case.com.
curly.test.case.com.              IN   CNAME    kwv001gate155.test.case.com.

I am not an authority on Netview's absolute DNS requirement but hope this
thread can get the experts to answer all of our questions. Anyway, hope this
helps.

Regards,
Ken Viola


"Todd H." wrote:

> Jane Curry <jane.curry@skills-1st.co.uk> writes:
> > I am quite sure that NetView uses name resolution for more than traps.
> > That said, it's an excellent idea to force your Ciscos to always send
> > traps from the loopback (you can't necessarily do this for ALL your
> > devices now and in the future, perhaps??)
>
> At the risk of asking a silly question....can anyone explain this
> concept of sending traps from the loopback interface?  I'm struggling
> at what this means.
>
> I'm familiar with a loopback address of 127.0.0.1, but as for loopback
> interface, I'm a bit lost.  Is this an administrative interface on
> Cisco devices that receives an IP address other than 127.0.0.1?
> Answers in the form of IOS commands cheerfully accepted.
>
> --
> Todd H.
> http://www.toddh.net/
> _________________________________________________________________________
> NV-L List information and Archives: http://www.tkg.com/nv-l

Todd,

The following is an excerpt from Cisco's public documentation and should help understand the nature and usage of loopback: (http://www.cisco.com/univercd/cc/td/doc/product/software/ios11/cbook/ciproute.htm#38888 and http://www.cisco.com/univercd/cc/td/doc/cisintwk/intsolns/as5xipmo/sysmgt.htm and http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/fun_r/frprt3/frd3001.htm#xtocid2988327)

Force the Router ID Choice with a Loopback Interface

OSPF uses the largest IP address configured on the router's interfaces as its router ID. If the interface associated with this IP address is ever brought down, or if the address is removed, the OSPF process must recalculate a new router ID and resend all of its routing information out its interfaces.

If a loopback interface is configured with an IP address, the router will use this IP address as its router ID, even if other interfaces have larger IP addresses. Since loopback interfaces never go down, greater stability in the routing table is achieved.

OSPF automatically prefers a loopback interface over any other kind, and it chooses the highest IP address among all loopback interfaces in the router. If no loopback interfaces are present, the highest IP address in the router is chosen. You cannot tell OSPF to use any particular interface.

To configure an IP address on a loopback interface, perform the following tasks, starting in global configuration mode:
  Task                                                                      Command
  Step 1 Create a loopback interface,                         interface loopback 0¹
which places you in interface configuration mode.

  Step 2 Assign an IP address to this interface.           ip address address mask²
 

  ¹This command is documented in the "Interface Commands" chapter of the Router Products Command Reference publication.
  ²This command is documented in the "IP Commands" chapter of the Router Products Command Reference publication.

snmp-server trap-source Loopback0  - Enables traps for unsolicited notifications for configuration changes, environmental variables, and device conditions.
 

A sample (name and IP changed to protect the innocent) config follows:

This example is for a router named 'kwv001gate155.test.case.com'

---router configuration sample---
!
hostname kwv001gate155
!
interface Loopback0
ip address 179.118.125.6 255.255.255.252
snmp-server trap-source  Loopback0
!

The following example is provided for reference for updating DNS. I know you didn't ask but it helps to describe my initial issue.

The forward entries would look like this:

kwv001gate155.test.case.com.    IN   A        179.118.125.6
                                                   IN   A        179.118.98.1
                                                   IN   A        179.118.98.65

(Note: the 2nd and 3rd ?A? records correspond to additional interfaces in the router and are not necessary if using the loopback address)

The reverse lookup entries would look like this:

6.125.118.179.IN-ADDR.ARPA.      IN   PTR      kwv001gate155.test.case.com.
1.98.118.179.IN-ADDR.ARPA.        IN   PTR      kwv001gate155.test.case.com.
65.98.118.179.IN-ADDR.ARPA.      IN   PTR      kwv001gate155.test.case.com.

(Note: the 2nd and 3rd ?PTR? records correspond to additional interfaces in the router and may not be necessary if using the loopback address)

Of course, it is also possible to create an alias or two for the router. The aliases would be put in the forward lookup file and would look something like this:

moe.test.case.com.              IN   CNAME    kwv001gate155.test.case.com.
larry.test.case.com.              IN   CNAME    kwv001gate155.test.case.com.
curly.test.case.com.              IN   CNAME    kwv001gate155.test.case.com.

I am not an authority on Netview's absolute DNS requirement but hope this thread can get the experts to answer all of our questions. Anyway, hope this helps.

Regards,
Ken Viola
 

"Todd H." wrote:

Jane Curry <jane.curry@skills-1st.co.uk> writes:
> I am quite sure that NetView uses name resolution for more than traps.
> That said, it's an excellent idea to force your Ciscos to always send
> traps from the loopback (you can't necessarily do this for ALL your
> devices now and in the future, perhaps??)

At the risk of asking a silly question....can anyone explain this
concept of sending traps from the loopback interface?  I'm struggling
at what this means.

I'm familiar with a loopback address of 127.0.0.1, but as for loopback
interface, I'm a bit lost.  Is this an administrative interface on
Cisco devices that receives an IP address other than 127.0.0.1?
Answers in the form of IOS commands cheerfully accepted.

--
Todd H.
http://www.toddh.net/
_________________________________________________________________________
NV-L List information and Archives: http://www.tkg.com/nv-l