From: Jim (nhatquang@thiennam.org)
Date: Wed Apr 06 2005 - 02:03:19 GMT-3
From CCO: "The offset value is added to the routing metric. An offset list
with an interface type and interface number is considered extended and takes
precedence over an offset list that is not extended."
so the offset is simply added to the cost. I think there's no relation to the
delay, distance or the number of hops for EIGRP here.
r4#sh ip route
Gateway of last resort is not set
132.1.0.0/16 is variably subnetted, 4 subnets, 2 masks
D 132.1.5.0/24 [90/40514560] via 132.1.45.5, 00:01:58, BRI0/0
r4(config-router)#offset-list 0 in 5000000
r4#conft
Gateway of last resort is not set
132.1.0.0/16 is variably subnetted, 4 subnets, 2 masks
D 132.1.5.0/24 [90/45514560] via 132.1.45.5, 00:01:21, BRI0/0
----- Original Message -----
From: Ed Lui
To: mani poopal
Cc: Brian Dennis ; John Matus ; ccielab@groupstudy.com
Sent: Wednesday, April 06, 2005 11:40 AM
Subject: Re: blocking eigrp routes
The result from my lab experience :
R2(config-router)#offset-list 2 out ?
<0-2147483647> Offset
The offset-list under eigrp add the value to the delay only.
Before the offset-list was : Total delay is 25000 microseconds
After the offset-list with 255 was : Total delay is 25009 microseconds
How did the 9 come from ? Hm !???
Edward Lui
On Apr 5, 2005 4:40 PM, mani poopal <mani_ccie@yahoo.com> wrote:
> Guys,
>
> You can make offset list to increase the metric and thereby can do a load
balancing.
> eg:
> R1 e0 -------------------------e0 R2 path1 eigrp metric 2115
> R1 e1--------------------------e1 R2 path2 eigrp metric 2005
> The routing table of R2 will have routes from R1 through only e1 of R1[due
to lower metric(not AD)]
> now on R1
> router eigrp xxx
> offset-list 0 110 in ethernet 1 -->Makes path 2 metric to
2115(2005+110) and make R1 routes appear as through both e0 and e1
> ps:other methods: variance, modifying bandwidth/delay(uneqal/equal cost
path load balancing)
>
> Mani
>
> Brian Dennis <bdennis@internetworkexpert.com> wrote:
> There is a hop count limitation in EIGRP but the offset list does not
> affect the number of hops for EIGRP.
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
>
> bdennis@internetworkexpert.com
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> John Matus
> Sent: Tuesday, April 05, 2005 4:02 PM
> To: ccie2be@nyc.rr.com; simon.hart@btinternet.com;
> ccielab@groupstudy.com
> Subject: RE: blocking eigrp routes
>
> i was under the impression, from what i have read in the past, that
> eigrp
> actually does consider a metric of 255 to be unreachable .
> in
> that situation i suppose you could use an offset list with a metric of
> 255,
> but mani seems to say differently.
> does anyone else recall eigrps hop limitations?
>
> >From: "ccie2be"
> >To: "'simon hart'" , "'John Matus'"
> >,
> >Subject: RE: blocking eigrp routes
> >Date: Tue, 5 Apr 2005 18:55:08 -0400
> >
> >Simon,
> >
> >I missed that. The doc-cd does say the value is added to the delay
> >component although not where you would expect it to say so. It's in
> >explanation of the example, not where they define what each variable of
> the
> >command does. Oh, well.
> >
> >As far as where to use this command, I did think of one scenario:
> >
> >Let's say you have to configure equal cost load-balancing and you're
> >prohibited from using any interface commands.
> >
> >To be sure, not a real world scenario, but not too unlikely a Cisco lab
> >task.
> >
> >What do ya think?
> >
> >Tim
> >
> >-----Original Message-----
> >From: simon hart [mailto:simon.hart@btinternet.com]
> >Sent: Tuesday, April 05, 2005 6:40 PM
> >To: ccie2be; 'John Matus'; ccielab@groupstudy.com
> >Subject: RE: blocking eigrp routes
> >
> >Tim,
> >
> >The Doc-CD does provide a hint
> >
> >http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr
> /fipr
> >rp_r/1rfeigrp.htm#wp1022565
> >
> >'For IGRP the offset is added to the delay component only'
> >
> >Now my assumption is that this is what also happens with EIGRP. If I
> get a
> >chance, and remember when I boot up my routers, I will test to see.
> With
> >that said, the offset will only be able to adjust one of the components
> for
> >the reasons stated before.
> >
> >When would you use eigrp offset ??? I am not sure either, have not
> seen up
> >come up as a requirement.
> >
> >Simon
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> >ccie2be
> >Sent: 05 April 2005 23:17
> >To: 'simon hart'; 'John Matus'; ccielab@groupstudy.com
> >Subject: RE: blocking eigrp routes
> >
> >
> >Simon,
> >
> >How interesting.
> >
> >Unfortunately, but as usual, the Doc-CD sheds no light on this. Did
> you
> >discover this by testing?
> >
> >I'm still trying to think of a scenario where using the offset command
> is
> >the only way to achieve the required result, but can't think of any.
> >
> >Have you come across any eigrp scenario's which would require this
> command
> >to be used?
> >
> >Tim
> >
> >-----Original Message-----
> >From: simon hart [mailto:simon.hart@btinternet.com]
> >Sent: Tuesday, April 05, 2005 6:05 PM
> >To: ccie2be; 'John Matus'; ccielab@groupstudy.com
> >Subject: RE: blocking eigrp routes
> >
> >Tim,
> >
> >I believe the offset is added to the delay component. The offset
> cannot be
> >the composite metric as the TLV's that eigrp advertised do not include
> the
> >composite value, but the delay, bandwidth, MTU, Load and Reliability
> (MTU
> >not used though!!). This is why the K values have to be the same
> througout
> >the domain.
> >
> >Now what I said below is was slightly incorrect (whoops!!). If the
> >originating route has a delay function of 1000, an offset list of 255
> will
> >in fact add 255 to that delay function, thus the delay will now be
> >advertised as 1255 to the next hop.
> >
> >Simon
> >
> >
> >
> >-----Original Message-----
> >From: ccie2be [mailto:ccie2be@nyc.rr.com]
> >Sent: 05 April 2005 22:50
> >To: 'simon hart'; 'John Matus'; ccielab@groupstudy.com
> >Subject: RE: blocking eigrp routes
> >
> >
> >Hi Simon,
> >
> >Excellent post!!!!
> >
> >But, you raise an interesting question.
> >
> >Given that eigrp has 2 types of metrics: bandwidth, delay, etc, and
> >composite, I assume that the metric used with the offset command is the
> >composite version, right?
> >
> >Now, normally with eigrp, whenever you manipulate metric values you're
> >manipulating the component (b/w, delay, etc,) values of the metric, not
> the
> >composite itself. So, what happens to the component values when you
> >manipulate the composite instead of the component values?
> >
> >Does eigrp use it's formula for computing the composite metric in
> reverse
> >when the composite itself is changed?
> >
> >Also, given what you've said, it seems like there's no good reason for
> >using
> >the offset-list command with eigrp.
> >
> >If you wanted or needed to change Eigrp's metric, for example, for the
> >purpose of load-balancing, you would change one of the component
> metrics
> >such as bandwidth or delay on the interfaces to do so rather than
> >manipulate
> >the composite metric with the offset command.
> >
> >So, what reason might there be for using the offset command?
> >
> >TIA, Tim
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> >simon hart
> >Sent: Tuesday, April 05, 2005 5:04 PM
> >To: John Matus; ccielab@groupstudy.com
> >Subject: RE: blocking eigrp routes
> >
> >Hi John,
> >
> >You cannot use the offset list to make a route(s) unreachable with
> eigrp,
> >although you can do this with rip.
> >
> >Rip has the philosophy that an infinite metric......anything over
> 15.....
> >is
> >unreachable, therefore making the metric 16 effectively makes those
> routes
> >effected by the offset list unreachable.
> >
> >Eigrp does not have the same philosophy, the composite metric in eigrp
> can
> >be anything and as far as the protocol is concerned it is still
> reachable
> >(within the confines fo FD's and FS's etc. etc.)
> >
> >The example you have given in RIP environment would dictate that every
> >route
> >advertised out of that interface would unreachable (bearing in mind
> that
> >you
> >could not use 255 in RIP, it would have to be 16). This really would
> seem
> >a
> >little pointless, may as well make the interface passive.
> >
> >If you used the example below for eigrp you would be advertising eigrp
> with
> >a metric of 255, and probably making those routes the most favourable.
> >Eigrp uses a composite metric, derived by default as function of
> bandwidth
> >and delay. The metrics are normally quite high, in fact a lot higher
> than
> >255 (for information the highest eigrp figure you can use on the offset
>
> >list
> >is 2147483647).
> >
> >In order not to advertise to the next hop router you could use:
> >
> >router eigrp 100
> >distribute-list 10 out s0/0
> >
> >access-list 10 deny 0.0.0.0 255.255.255.255
> >
> >Change the access list if you wish to deny a subset of routes.
> >
> >HTH
> >
> >Simon
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> >John Matus
> >Sent: 05 April 2005 21:30
> >To: ccielab@groupstudy.com
> >Subject: blocking eigrp routes
> >
> >
> >if i wanted to block all eigrp routes from exiting to the next hop
> would it
> >be:
> >
> >offset-list 1 out 255 s0/0
> >
> >access-l 1 permit 0.0.0.0 255.255.255.255 ?
> >
> >i wasn't sure since rip's metric would be '16' for offset but i'm not
> sure
> >about eigrp.
> >thanks in advance
> >
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