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DarkFiber

EIGRP

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Any more questions guys :)

 

Hi Brian, Glad your here

 

What are your thoughts on this one ?

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What are your thoughts on this one ?

 

Hello Laf_c,

 

Remember that even thou the EIGRP is a hybrid protocol,having some characteristics from Link-state, it doesn't work in its routing updates exactly like OSPF/ISIS, it doesn't fwd all its exact topology like OPSF,in this topology R3 will send only the Successor to R0.

 

if your network is running OSPF then inside the SPF database you will find on R0

 

P 192.168.1.0/24, FD is 2.5 ( with respect to OSPF metric, its just an example)

via R3 (2.5/1.5)

via R3 (3/2).

 

If your nteowrk is running EIGRP , then inside EIGRP topology table you will find on R0

 

P 192.168.1.0/24, FD is 2.5

via R3 (2.5/1.5)

 

 

Thats my thoughts Kindly lab it and check to confirm.

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Thanks for sharing such a wonderful document ....

 

 

 

Regards,

 

Thanks :)

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This has helped a lot with my EIGRP studies the past few weeks, thanks!

 

Your Welcome :)

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Hi @DarkFiber,

 

Thanks for share if you have BGP Notes like this kindly share.

 

Hello Talal, will do my best to prepare it & post it ASAP

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a question about hello/hold timers:

Interestingly, the Hello and Hold time parameters do not need to match for EIGRP neighbor

relationships to form. In fact, a router does not use its own timers when monitoring a neighbor

relationship—instead, it uses each neighbor’s stated timers, as exchanged in the Hello messages.

is this true? I could not see reflected changes with show ip eigrp interface detail interface. If so, if 2 neighbors share different timers, whose time is going to be used? The one who sent the first hello packet?

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a question about hello/hold timers:

 

is this true? I could not see reflected changes with show ip eigrp interface detail interface. If so, if 2 neighbors share different timers, whose time is going to be used? The one who sent the first hello packet?

 

The lowest, like BGP.

Also this may be modified using IOS code....i mean this can be changed or vary based on IOS version.

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<!--coloro:#FF0000--><span style="color:#FF0000"><!--/coloro--><b>EIGRP Summary</b><!--colorc--></span><!--/colorc-->

 

<!--coloro:#FF8C00--><span style="color:#FF8C00"><!--/coloro--><b>The characteristics of EIGRP follow:</b><!--colorc--></span><!--/colorc-->

 

 Hybrid routing protocol (distance vector that has link-state protocol characteristics).

 

 Use DUAL, first proposed by E. W. Dijkstra and C. S. Scholten, to perform distributed shortest-path routing while maintaining freedom from loops at every instant. Although many researchers have contributed to the development of DUAL, the most prominent work is that of J. J. Garcia-Luna-Aceves.

 

 Cisco Proprietary created in 1994.

 

 First released in IOS 9.21

 

 Uses IP protocol 88.

 

 Makes Automatic summarization on network Class boundary.

 

 Classless protocol (supports VLSMs).

 

 Have the power to shut the Auto-summarization And make a configured manual Summarization.

 

 Default composite metric of bandwidth and delay.

 

 You can factor load, MTU and reliability into the metric.

 

 Eigrp metric is the same as IGRP*256, It uses the smallest B.W,Reliablity,Load & MTU with the Comulative delay upon the path…..The MTU doesn’t actually used in the Metric calculations, But is included in the EIGRP Routing updates.

 

 Sends route updates to multicast address 224.0.0.10, and nei. Reply’s back with Unicast Address.

 

 Sends non-periodic, partial, and bounded updates.

 

 Send Hello packets every 5 sec. and Hold down timer is 15 sec.

 

 For Low speed Hello is every 60 sec. with hold down time 180 sec.

 

 By default, EIGRP uses no more than 50 percent of the bandwidth of a link.

 

 Support for authentication via MD5 Only.

 

 Uses DUAL for loop prevention, and generating Succ./Fesible Succ.

 

 Maximum paths for Load-balancing are 6 & default is 4 , maximum are 16 in IOS 12.3(2)T and later IOS releases, And i heard its 24 in newest releases..loool

 

 By default, Equal-Metric load balancing. If Unequal-Metric load sharing is used the router will load share inversely proportional to the metrics of the paths.

 

 Administrative distance is 90 for EIGRP internal routes, 170 for EIGRP external routes, and 5 for EIGRP summary routes.

 

 Potential routing protocol for the core of a network; used in large networks.

 

 For neighbor relation to be established, both routers must send and receive Hello or Ack packets from each other, they must have the same AS #, and the same Metric K values.

 

 Eigrp doesn’t restrict that neighbors must have the same Hello & dead interval timers, Unlike OSPF.

 

 Has a Maximum hop count of 255, the default is 100 in the last IOS releases.

 

 

Check attachment for metric calculations & extra info about the Dual & cmds

 

 

 

 

thank u so much for this informative meterial. i m confuse abt multicast flow timer, retransmission timeout(RTO) and smooth round trip time(SRTT). write a brief note on these topis which should be understandable for all. waiting for reply .. and again thank u for this summry

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thank u so much for this informative meterial. i m confuse abt multicast flow timer, retransmission timeout(RTO) and smooth round trip time(SRTT). write a brief note on these topis which should be understandable for all. waiting for reply .. and again thank u for this summry

 

I recommend you read this Topic on Jeff Doyle book , Routing TCP/IP, it has full details......sorry for not replying with details, as i have limited access to the internet as im in my Honey Moon now ;)

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Hi friends, A very basic question which could be helpful for me to concrete my concepts.

R2-----------R3 are connected over Ethernet.

R3-----------R4 connected to each other over serial interface and running EIGRP.

when I do "show ip protocols", i see R3 and R4 are the "gateway" to each other but R2 has no gateway.

My question is can R3 be the gateway of R2? If not then please justify it. A detailed reply on this topic will be highly appreciated.

 

 

Take care!

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Can anyone write down exactly definition of feasible successor, cause as i know it is formulated in such way:

 

feasible successor = backup router with loop-free path ( AD of feasible successor must be less that FD current successor route).

 

 

Thats how Cisco defines, but in some cases i found that AD of feasible successor must be less OR EQUAL that FD current successor route.

 

So must it be just less or it can be equal as well???

 

 

Thanks

Edited by kaxa
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Can anyone write down exactly definition of feasible successor, cause as i know it is formulated in such way:

 

feasible successor = backup router with loop-free path ( AD of feasible successor must be less that FD current successor route).

 

 

Thats how Cisco defines, but in some cases i found that AD of feasible successor must be less OR EQUAL that FD current successor route.

 

So must it be just less or it can be equal as well???

 

 

Thanks

 

Dear Kaxa,

 

Feasible successor is the route and not router. And you must remember that AD MUST BE LESS THEN FD to meet the FC. if AD is equal or greater then FD, then it will not be a feasible successor. Keep in mind, that EIGRP process first identifies all the feasible successor routes (routes with their AD < FD) and the lowest of them becomes the successor route.

 

Hope this helps

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Here is attached picture, how you think why is answer choice E.) and not choice B.)

 

 

Can anyone explain?

post-134120-097031600 1276673187_thumb.jpg

Edited by kaxa
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It's obvious it's that those 3 routers would communicate (ie - ping). It has nothing to do with authentication. If you pay attention you will see that key-strings match like they suppose to.

 

Regarding EIGRP authentication - I'd have a question though.

 

I've read in the new route documentation that

" EIGRP authentication configuration process requires several commands, which are summarized as follows:

 

Step 1. Create an (authentication) key chain:

 

- Create the chain and give it a name with the key chain name global command (also puts the user into key chain config mode). The name does not have to match on the neighboring routers.

- Create one or more key numbers using the key number command in key chain configuration mode. The key numbers do not have to match on the neighboring routers.!!!!

- Define the authentication key’s value using the key-string value command in key configuration mode. The key strings must match on the neighboring routers.

- (Optional) Define the lifetime (time period) for both sending and accepting each key string.

 

Step 2. Enable EIGRP MD5 authentication on an interface, for a particular EIGRP ASN, using the ip authentication mode eigrp asn md5 interface subcommand.

 

Step 3. Refer to the correct key chain to be used on an interface using the ip authentication key-chain eigrp asn name-of-chain interface subcommand"

 

This is wrong! If you're setting up the same key-string using diffrent key-id's, the routers won't communicate because they won't find a key with that specifically id to check (when authentication is configured a hash is made from message, keyid and password that is the key-string)

 

How do you think about it?

Edited by 0ctavianus
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It's obvious it's that those 3 routers would communicate (ie - ping). It has nothing to do with authentication. If you pay attention you will see that key-strings match like they suppose to.

 

Regarding EIGRP authentication - I'd have a question though.

 

I've read in the new route documentation that

" EIGRP authentication configuration process requires several commands, which are summarized as follows:

 

Step 1. Create an (authentication) key chain:

 

- Create the chain and give it a name with the key chain name global command (also puts the user into key chain config mode). The name does not have to match on the neighboring routers.

- Create one or more key numbers using the key number command in key chain configuration mode. The key numbers do not have to match on the neighboring routers.!!!!

- Define the authentication key’s value using the key-string value command in key configuration mode. The key strings must match on the neighboring routers.

- (Optional) Define the lifetime (time period) for both sending and accepting each key string.

 

Step 2. Enable EIGRP MD5 authentication on an interface, for a particular EIGRP ASN, using the ip authentication mode eigrp asn md5 interface subcommand.

 

Step 3. Refer to the correct key chain to be used on an interface using the ip authentication key-chain eigrp asn name-of-chain interface subcommand"

 

This is wrong! If you're setting up the same key-string using diffrent key-id's, the routers won't communicate because they won't find a key with that specifically id to check (when authentication is configured a hash is made from message, keyid and password that is the key-string)

 

How do you think about it?

 

 

Lab it up & tell us back ;)

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One thing I'm worried for EIGRP after the field is not working Next Hop Hop RIPv2 OSPF and shipping address. Please investigate this matter when you free. Thanks.

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Hello,

 

I hope you don't mind reopening an old post, I have a question regarding EIGRP. I saw that summary routes have AD of 5. But I can't get any summary routes. Actually they shows as normal internal route with AD=90:

 

I added command under interface: ip summary-address eigrp 1 1.1.1.0 255.255.255.252 5 (5 was actually added automatically)

and then ip route 1.1.1.0 255.255.255.252 Null0

 

and route appear on neighbor router, but AD=90

D 1.1.1.0/30 [90/28160] via 192.168.4.1, 00:05:53, FastEthernet0/0

 

R4#sh ip route 1.1.1.0 255.255.255.252

Routing entry for 1.1.1.0/30

Known via "eigrp 1", distance 90, metric 28160, type internal

 

what have I missed?:)

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Hello ZigAA,

 

I was running into the same question right now. I hope you already found the answer long ago but just in case anyone else has the same doubt... The AD=5 for summary routes is only valid locally, in the router doing the summarization. Once advertised it is like any other route, so AD=90 in the neighbor receiving the route.

 

BR

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Hello ZigAA,

 

I was running into the same question right now. I hope you already found the answer long ago but just in case anyone else has the same doubt... The AD=5 for summary routes is only valid locally, in the router doing the summarization. Once advertised it is like any other route, so AD=90 in the neighbor receiving the route.

 

BR

 

Dears, kindly be advised that AD is locally generated, it can also be edited, BUT AD value is NEVER sent in any fields in the routing updates. ;)

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EIGRP authentication configuration process requires several commands, which are summarized as follows:

...

- Create one or more key numbers using the key number command in key chain configuration mode. The key numbers do not have to match on the neighboring routers.!!!!

...

How do you think about it?

Completely agree with said above. Additional description (with debug output) can be found on LinkedIn.com and PasteBin.com.

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