From: Scott M Vermillion (scott_ccie_list@it-ag.com)
Date: Sun Nov 30 2008 - 22:41:41 ARST
Just for the heck of it, here's an IP Internal Route update being received
on R4 from R5 via HDLC (this network is locally attached to R5):
No. Time Source Destination Protocol
Info
13 5.811533 10.0.45.5 10.0.45.4 EIGRP
Update
Frame 13 (72 bytes on wire, 72 bytes captured)
Cisco HDLC
Internet Protocol, Src: 10.0.45.5 (10.0.45.5), Dst: 10.0.45.4 (10.0.45.4)
Cisco EIGRP
Version = 2
Opcode = 1 (Update)
Checksum = 0x9b29
Flags = 0x00000008
Sequence = 10
Acknowledge = 12
Autonomous System : 100
IP internal route = 10.0.35.0/24
Type = 0x0102 (IP internal route)
Size = 28 bytes
Next Hop = 0.0.0.0
Delay = 2560
Bandwidth = 25600
MTU = 1500
Hop Count = 0
Reliability = 255
Load = 1
Reserved
Prefix Length = 24
Destination = 10.0.35.0
And then that same internal route being received on R1 from R4 via FR:
No. Time Source Destination Protocol
Info
33 45.578414 10.0.12.2 10.0.12.1 EIGRP
Update
Frame 33 (72 bytes on wire, 72 bytes captured)
Frame Relay
Internet Protocol, Src: 10.0.12.2 (10.0.12.2), Dst: 10.0.12.1 (10.0.12.1)
Cisco EIGRP
Version = 2
Opcode = 1 (Update)
Checksum = 0xe301
Flags = 0x00000000
Sequence = 29
Acknowledge = 7
Autonomous System : 100
IP internal route = 10.0.35.0/24
Type = 0x0102 (IP internal route)
Size = 28 bytes
Next Hop = 0.0.0.0
Delay = 514560
Bandwidth = 1657856
MTU = 1500
Hop Count = 1
Reliability = 255
Load = 1
Reserved
Prefix Length = 24
Destination = 10.0.35.0
Just as a weird side note, you see "Version = 2" in all EIGRP packets. But
check out a hello (look at "EIGRP Release Version" at the very bottom:
No. Time Source Destination Protocol
Info
24 43.535115 10.0.12.2 224.0.0.10 EIGRP
Hello
Frame 24 (64 bytes on wire, 64 bytes captured)
Frame Relay
Internet Protocol, Src: 10.0.12.2 (10.0.12.2), Dst: 224.0.0.10 (224.0.0.10)
Cisco EIGRP
Version = 2
Opcode = 5 (Hello)
Checksum = 0xedc3
Flags = 0x00000000
Sequence = 0
Acknowledge = 0
Autonomous System : 100
EIGRP Parameters
Type = 0x0001 (EIGRP Parameters)
Size = 12 bytes
K1 = 1
K2 = 0
K3 = 1
K4 = 0
K5 = 0
Reserved
Hold Time = 180
Software Version: IOS=12.4, EIGRP=1.2
Type = 0x0004 (Software Version)
Size = 8 bytes
IOS release version = 12.4
EIGRP release version = 1.2
Strange...
-----Original Message-----
From: Scott M Vermillion [mailto:scott_ccie_list@it-ag.com]
Sent: Sunday, November 30, 2008 5:12 PM
To: 'paul cosgrove'; 'Timothy Chin'
Cc: 'Oleg Konovalov'; 'Cisco certification'
Subject: RE: EIGRP Maximum-hop
Hi again Paul!
Hop count is actually carried in the EIGRP "IP Internal Routes TLV" and the
"IP External Routes TLV" (Doyle Vol I is a great reference for this and
similar such topics). A router advertises a directly connected network with
a hop count of zero and it's incremented from there by subsequent routers
learning of that network. When a router receiving an update increments hop
count and the resulting value exceeds the locally configured max-hop value,
it will be marked unreachable with a delay of 0xFFFFFF. I don't believe
that any update is sent on regarding that route with a delay of 0xFFFFFF - I
believe this to be a completely local affair on a router-by-router basis.
But I could be wrong on that last count. Semantics at that point anyway.
So I'd think that you'd either need a really big EIGRP network to test what
the truly maximum implemented value might be or you'd need a means to
manipulate the "Hop Count" field in the TLV. I'm not aware that this can be
manipulated in a route-map or any such thing...
Cheers,
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of paul
cosgrove
Sent: Sunday, November 30, 2008 2:29 PM
To: Timothy Chin
Cc: Oleg Konovalov; Cisco certification
Subject: Re: EIGRP Maximum-hop
p.s. I should have said we need to set maximum hops to 255 and generate a
packet as if it has passed over >224 hops. IPv6 hop limit, like TTL, count
down not up.
On Sun, Nov 30, 2008 at 9:15 PM, paul cosgrove
<paul.cosgrove@gmail.com>wrote:
> Hi Timothy,
Blogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4
: Mon Dec 01 2008 - 08:18:32 ARST
>
> Thanks for the link. The paragraph which explains the 224 limit is
> 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/
f>
>
publications/interop94.pdf<http://ccrg.soe.ucsc.edu/publications/interop94.p
df>
> 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.
>
> Since the documentation about the max hop limit is conflicting, some of it
> 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.
>
> Paul.
>
>
> On Sun, Nov 30, 2008 at 7:05 PM, Timothy Chin <Tim@1c-solutions.com>wrote:
>
>> Hi,
>>
>>
>>
>> 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_ps644
1_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_paper09186a00
80094cb>
>> 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
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html