From: paul cosgrove (paul.cosgrove@gmail.com)
Date: Sun Nov 30 2008 - 19:15:12 ARST
Hi Timothy,
Thanks for the link. The paragraph which explains the 224 limit is
Since the documentation about the max hop limit is conflicting, some of it
Paul.
On Sun, Nov 30, 2008 at 7:05 PM, Timothy Chin <Tim@1c-solutions.com> wrote:
> Hi,
Blogs and organic groups at http://www.ccie.net
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: Mon Dec 01 2008 - 08:18:32 ARST
incorrect in that the Transport Control Field does not exist in IP or IPv6
headers. The IPX TC header field functions like a hop count, and IPX
packets with a TC of 16 are dropped, hence the need for a workaround if
packets need to be sent further. The TTL in IP, or hop limit in IPv6 both
allow 255 hops so there is no need to do that.
The text looks to have been incorrectly copied from the old documentation.
The IPX workaround is explained in the old EIGRP paper at
http://ccrg.soe.ucsc.edu/
publications/interop94.pdf<http://ccrg.soe.ucsc.edu/publications/interop94.pdf>
and all the references I've seen to 224 appear to have been derived/copied
from that text. I've left a comment on the web page that it needs updating.
must be incorrect. My guess is that the limit is indeed 255, but the only
way we will know for sure is to generate an eigrp packet with the hop limit
set above 224 and see if other routers consider the advertisement as valid.
>
>
>
> I know there has been conflicting information on this for awhile. I don't
> know why but the 12.4 command reference for IPv4 doesn't provide this
> information but the IPv6 reference does specify the maximum network width:
>
>
>
>
> http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-eigrp_ps6441_TSD_Products_Configuration_Guide_Chapter.html
>
>
>
> I don't see an update on the 12.4 IPv4 documentation regarding this but
> going by previous releases I figure it would still be the same. From what I
> know a maximum hop count of 255 can be configured but traffic would only
> traverse 224.
>
>
> ------------------------------
>
> *From:* paul cosgrove [mailto:paul.cosgrove@gmail.com]
> *Sent:* Sunday, November 30, 2008 12:56 PM
> *To:* Timothy Chin
> *Cc:* Oleg Konovalov; Cisco certification
> *Subject:* Re: EIGRP Maximum-hop
>
>
>
> Hi Timothy,
>
> Just wondering if you have verified that?
>
> I know there is conflicting information about this point but the 12.4
> command reference says the limit is 255.
>
> http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_eig2.html#wp1011619
>
> Also the field is indeed 8 bits long in the packets (see figure 4-7).
> http://oreilly.com/catalog/iprouting/chapter/ch04.html
>
> The following paper mentions the limit of 224, but only as a workaround
> used on IPX networks to overcome limitations of IPX.
> http://ccrg.soe.ucsc.edu/publications/interop94.pdf
>
> Paul.
>
> On Sun, Nov 30, 2008 at 12:49 PM, Timothy Chin <Tim@1c-solutions.com>
> wrote:
>
> The maximum definable hop count is 255 but 224 hops is the true limit.
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Oleg Konovalov
> Sent: Sunday, November 30, 2008 5:05 AM
> To: Cisco certification
> Subject: EIGRP Maximum-hop
>
> Hi all, I have question about EIGRP maximum hops, based on
> http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080
> 094cb<http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb>
> 7.shtml we can set up maximum 220 hops, based on some CCNP materials it
> is
> 224. I test it on my router and 255 hops was OK.
>
> Routing Protocol is "eigrp 100"
> Outgoing update filter list for all interfaces is not set
> Incoming update filter list for all interfaces is not set
> Default networks flagged in outgoing updates
> Default networks accepted from incoming updates
> EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
> EIGRP maximum hopcount 100
> EIGRP maximum metric variance 1
> Redistributing: eigrp 100
> EIGRP NSF-aware route hold timer is 240s
> Automatic network summarization is in effect
> Maximum path: 4
> Routing for Networks:
> Routing Information Sources:
> Gateway Distance Last Update
> Distance: internal 90 external 170
>
>
> Then I have changed metric maximum-hops
>
> Router(config)#router eigrp 100
> Router(config-router)#metric maximum-hops 255
> Router(config-router)#end
> Router#sh ip protocols
> Routing Protocol is "eigrp 100"
> Outgoing update filter list for all interfaces is not set
> Incoming update filter list for all interfaces is not set
> Default networks flagged in outgoing updates
> Default networks accepted from incoming updates
> EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
> EIGRP maximum hopcount 255
> EIGRP maximum metric variance 1
> Redistributing: eigrp 100
> EIGRP NSF-aware route hold timer is 240s
> Automatic network summarization is in effect
> Maximum path: 4
> Routing for Networks:
> Routing Information Sources:
> Gateway Distance Last Update
> Distance: internal 90 external 170
>
>
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