RIp Hop Count

[Ahmed Mukhtar]

Hello and Good Evening

                           My Question is really simple...... Why does Rip has a HOP count limit of 15? any technical reason apart from that it is desgined for small size 

network... and Can we tweak or change this behavior by any means? ? like can we.....go insane and change the MAX Hop count to 5 or 6 or any larger

value then 15 ??

So much for simplicity 

Thank You 

Ahmed Mukhtar

[Bilal Nawaz]

Hello Ahmed,

In RIP -

Maximum of 15 hops, and 16 is considered an infinite distance and therefor unreachable. This is mainly due to preventing routing loops, remember RIP is slow and old, it does not converge quickly and may end up looping a network. RIP implements the Split Horizon, Poison Reverse and hold-down mechanisms to prevent bad routing information from being advertised in some cases, learned too.

Here are the limitations on RIPv2 according to RFC 2453:

 https://tools.ietf.org/html/rfc2453

3.2 Limitations of the Protocol

This protocol does not solve every possible routing problem. As mentioned above, it is primary intended for use as an IGP in networks of moderate size. In addition, the following specific limitations are be mentioned:

- The protocol is limited to networks whose longest path (the network's diameter) is 15 hops. The designers believe that the basic protocol design is inappropriate for larger networks. Note that this statement of the limit assumes that a cost of 1 is used for each network. This is the way RIP is normally configured. If the system administrator chooses to use larger costs, the upper bound of 15 can easily become a problem.

- The protocol depends upon "counting to infinity" to resolve certain unusual situations. (This will be explained in the next section.) If the system of networks has several hundred networks, and a routing loop was formed involving all of them, the resolution of the loop would require either much time (if the frequency of routing updates were limited) or bandwidth (if updates were sent whenever changes were detected). Such a loop would consume a large amount of network bandwidth before the loop was corrected. We believe that in realistic cases, this will not be a problem except on slow lines. Even then, the problem will be fairly unusual, since various precautions are taken that should prevent these problems in most cases.

- This protocol uses fixed "metrics" to compare alternative routes. It is not appropriate for situations where routes need to be chosen based on real-time parameters such a measured delay, reliability, or load. The obvious extensions to allow metrics of this type are likely to introduce instabilities of a sort that the protocol is not designed to handle.

hth

[Joseph W. Doherty]

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Posting

My guess is RIP's hop count only allocated 4 bits.

If I'm correct, RIP hop count could have be made bigger, but as RIP alreadly has scalability issues with a hop count of 15, it's designers probably thought a better routing protocol should be used for larger networks.  (And we do have better routing protocols for larger netoworks, e.g. OSPF, IS-IS and BGP.)

[paul driver]

Hello

You are correct  - Rip was designed for small networks and is the oldest of the distance vector routing protocols such as IGRP/EIGRP..

You can also manipulate the rip hop count in such away that prefixes are advertised as a less attractive path using metric and offset statements - however I not aware of actually changing the maximum default rip hop count of 15 (16 meaning inaccessible)

　

res

Paul

[abdelfatahelarfaoui]

Hello Ahmed

It's the only way to stop such "routing by rumor" protocol so if the hop count is not limited it will cause performance issues

@Joseph Doherty: Hop count is the metric of RIP so it's 32 bits

Abdelfatah

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Well that what happens one when guesses instead of examining the RFC.

It's surprising that allocation is so large compared to the metric limit.  Still, I suspect part of choosing 16 was to allow working the metric as a nibble.

Oh, and since this time I actually looked at the RFC, 1058, there's a part that addresses the OP's original question.

      - The protocol is limited to networks whose longest path
        involves 15 hops.  The designers believe that the basic
        protocol design is inappropriate for larger networks.  Note
        that this statement of the limit assumes that a cost of 1
        is used for each network.  This is the way RIP is normally
        configured.  If the system administrator chooses to use
        larger costs, the upper bound of 15 can easily become a
        problem.

[nitinm001]

Hi Ahmed,

As Rip is very old and mainly used to small network. That's why it can only be used in that environment where only 14 or 15 routers are available. When 16th router will add in network it will not be reachable.