As per Relevance of the word multicast, we have this rfc below:
Network Working Group G.
Request for Comments: 1388 Xylogics, Inc
Updates: RFC 1058 January 1993
RIP Version 2
Carrying Additional
Status of this
This RFC specifies an IAB standards track protocol for the
community, and requests discussion and suggestions for improvements
Please refer to the current edition of the "IAB Official
Standards" for the standardization state and status of this protocol
Distribution of this memo is unlimited
This document specifies an extension of the Routing
Protocol (RIP), as defined in [1], to expand the amount of
information carried in RIP packets and to add a measure of security
A companion document will define the SNMP MIB objects for RIP-2 [2].
I would like to thank the following for their contributions to
document: Fred Baker, Noel Chiappa and Vince Fuller. This memo is
product of the RIP-2 Working Group of the Internet Engineering
Force (IETF).
Table of
1. Justification . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Current RIP . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . . 2
3.1 Authentication . . . . . . . . . . . . . . . . . . . . . . . 3
3.2 Routing Domain . . . . . . . . . . . . . . . . . . . . . . . 4
3.3 Route Tag . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.4 Subnet Mask . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.5 Next Hop . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.6 Multicasting . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1 Compatibility Switch . . . . . . . . . . . . . . . . . . . . 5
4.2 Authentication . . . . . . . . . . . . . . . . . . . . . . . 6
4.3 Larger Infinity . . . . . . . . . . . . . . . . . . . . . . . 6
4.4 Addressless Links . . . . . . . . . . . . . . . . . . . . . . 6
Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Malkin [Page 1]
RFC 1388 RIP Version 2 January 1993
Security Considerations . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.
With the advent of OSPF and IS-IS, there are those who believe
RIP is obsolete. While it is true that the newer IGP
protocols are far superior to RIP, RIP does have some advantages
Primarily, in a small network, RIP has very little overhead in
of bandwidth used and configuration and management time. RIP is
very easy to implement, especially in relation to the newer IGPs
Additionally, there are many, many more RIP implementations in
field than OSPF and IS-IS combined. It is likely to remain that
for some years yet
Given that RIP will be useful in many environments for some period
time, it is reasonable to increase RIP's usefulness. This
especially true since the gain is far greater than the expense of
change
2. Current
The current RIP packet contains the minimal amount of
necessary for routers to route packets through a network. It
contains a large amount of unused space, owing to its origins
The current RIP protocol does not consider autonomous systems
IGP/EGP interactions, subnetting, and authentication
implementations of these postdate RIP. The lack of subnet masks is
particularly serious problem for routers since they need a
mask to know how to determine a route. If a RIP route is a
route (all non-network bits 0), the subnet mask equals the
mask. However, if some of the non-network bits are set, the
cannot determine the subnet mask. Worse still, the router
determine if the RIP route is a subnet route or a host route
Currently, some routers simply choose the subnet mask of
interface over which the route was learned and determine the
type from that
3. Protocol
This document does not change the RIP protocol per se. Rather,
provides extensions to the datagram format which allows routers
share important additional information
Malkin [Page 2]
RFC 1388 RIP Version 2 January 1993
The new RIP datagram format is
0 1 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Command (1) | Version (1) | Routing Domain (2) |
+---------------+---------------+-------------------------------+
| Address Family Identifier (2) | Route Tag (2) |
+-------------------------------+-------------------------------+
| IP Address (4) |
+---------------------------------------------------------------+
| Subnet Mask (4) |
+---------------------------------------------------------------+
| Next Hop (4) |
+---------------------------------------------------------------+
| Metric (4) |
+---------------------------------------------------------------+
The Command, Address Family Identifier (AFI), IP Address, and
all have the meanings defined in RFC 1058. The Version field
specify version number 2 for RIP datagrams which use
or carry information in any of the newly defined fields
All fields are coded in IP network byte order (big-endian).
3.1
Since authentication is a per packet function, and since there
only one 2-byte field available in the packet header, and since
reasonable authentication scheme will require more than two bytes
the authentication scheme for RIP version 2 will use the space of
entire RIP entry. If the Address Family Identifier of the first (
only the first) entry in the packet is 0xFFFF, then the remainder
the entry contains the authentication. This means that there can be
at most, 24 RIP entries in the remainder of the packet.
authentication is not in use, then no entries in the packet
have an Address Family Identifier of 0xFFFF. A RIP packet
contains an authentication entry would have the following format
0 1 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Command (1) | Version (1) | Routing Domain (2) |
+---------------+---------------+-------------------------------+
| 0xFFFF | Authentication Type (2) |
+-------------------------------+-------------------------------+
~ Authentication (16) ~
+---------------------------------------------------------------+
Malkin [Page 3]
RFC 1388 RIP Version 2 January 1993
Currently, the only Authentication Type is simple password and it
type 2. The remaining 16 bytes contain the plain text password.
the password is under 16 bytes, it must be left-justified and
to the right with nulls (0x00).
3.2 Routing
The Routing Domain (RD) number is the number of the routing
to which this update belongs. This field is used to associate
routing update to a specific routing process on the receiving router
The RD is needed to allow multiple, independent RIP "clouds" to co
exist on the same physical wire. This gives administrators
ability to run multiple, possibly parallel, instances of RIP in
to implement simple policy. This means that a router
within one routing domain, or a set of routing domains, should
RIP packets which belong to another routing domain. RD 0 is
default routing domain
3.3 Route
The Route Tag (RT) field exists as a support for EGPs. The
and use of this field are outside the scope of this protocol
However, it is expected that the field will be used to
Autonomous System numbers for EGP and BGP. Any RIP system
receives a RIP entry which contains a non-zero RT value must re
advertise that value. Those routes which have no RT value
advertise an RT value of zero
3.4 Subnet
The Subnet Mask field contains the subnet mask which is applied
the IP address to yield the non-host portion of the address. If
field is zero, then no subnet mask has been included for this entry
On an interface where a RIP-1 router may hear and operate on
information in a RIP-2 routing entry the following two rules apply
1) information internal to one network must never be advertised
another network,
2) information about a more specific subnet may not be
where RIP-1 routers would consider it a host route
3.5 Next
The immediate next hop IP address to which packets to the
specified by this route entry should be forwarded. Specifying
value of 0.0.0.0 in this field indicates that routing should be
Malkin [Page 4]
RFC 1388 RIP Version 2 January 1993
the originator of the RIP advertisement. An address specified as
next hop must, per force, be directly reachable on the logical
over which the advertisement is made
The purpose of the Next Hop field is to eliminate packets
routed through extra hops in the system. It is particularly
when RIP is not being run on all of the routers on a network.
simple example is given in Appendix A. Note that Next Hop is
"advisory" field. That is, if the provided information is ignored,
possibly sub-optimal, but absolutely valid, route may be taken
3.6
In order to reduce unnecessary load on those hosts which are
listening to RIP-2 packets, an IP multicast address will be used
periodic broadcasts. The IP multicast address is 224.0.0.9.
that IGMP is not needed since these are inter-router messages
are not forwarded
In order to maintain backwards compatibility, the use of
multicast address will be configurable, as described in section 4.1.
If multicasting is used, it should be used on all interfaces
support it
4.
RFC 1058 showed considerable forethought in its specification of
handling of version numbers. It specifies that RIP packets
version 0 are to be discarded, that RIP packets of version 1 are
be discarded if any Must Be Zero (MBZ) field is non-zero, and
RIP packets of any version greater than 1 should not be
simply because an MBZ field contains a value other than zero.
means that the new version of RIP is totally backwards
with existing RIP implementations which adhere to this part of
specification
4.1 Compatibility
A compatibility switch is necessary for two reasons. First,
are implementations of RIP-1 in the field which do not follow
1058 as described above. Second, the use of multicasting
prevent RIP-1 systems from receiving RIP-2 updates (which may be
desired feature in some cases).
The switch has three settings: RIP-1, in which only RIP-1 packets
sent; RIP-1 compatibility, in which RIP-2 packets are broadcast;
RIP-2, in which RIP-2 packets are multicast. The recommended
for this switch is RIP-1 compatibility
Malkin [Page 5]
RFC 1388 RIP Version 2 January 1993
4.2
Since an authentication entry is marked with an Address
Identifier of 0xFFFF, a RIP-1 system would ignore this entry since
would belong to an address family other than IP. It should be noted
therefore, that use of authentication will not prevent RIP-1
from seeing RIP-2 packets. If desired, this may be done
multicasting, as described in sections 3.6 and 4.1.
4.3 Larger
While on the subject of compatibility, there is one item which
have requested: increasing infinity. The primary reason that
cannot be done is that it would violate backwards compatibility.
larger infinity would obviously confuse older versions of rip.
best, they would ignore the route as they would ignore a metric
16. There was also a proposal to make the Metric a single byte
reuse the high three bytes, but this would break any
which treat the metric as a long
4.4 Addressless
As in RIP-1, addressless links will not be supported by RIP-2.
Appendix
This is a simple example of the use of the next hop field in a
entry
----- ----- ----- ----- ----- -----
|IR1| |IR2| |IR3| |XR1| |XR2| |XR3|
--+-- --+-- --+-- --+-- --+-- --+--
| | | | | |
--+-------+-------+---------------+-------+-------+--
<-------------RIP-2------------->
Assume that IR1, IR2, and IR3 are all "internal" routers which
under one administration (e.g., a campus) which has elected to
RIP-2 as its IGP. XR1, XR2, and XR3, on the other hand, are
separate administration (e.g., a regional network, of which
campus is a member) and are using some other routing protocol (e.g.,
OSPF). XR1, XR2, and XR3 exchange routing information
themselves such that they know that the best routes to networks N
and N2 are via XR1, to N3, N4, and N5 are via XR2, and to N6 and N
are via XR3. By setting the Next Hop field correctly (to XR2
N3/N4/N5, to XR3 for N6/N7), only XR1 need exchange RIP-2 routes
IR1/IR2/IR3 for routing to occur without additional hops through XR1.
Without the Next Hop (for example, if RIP-1 were used) it would
Malkin [Page 6]
RFC 1388 RIP Version 2 January 1993
necessary for XR2 and XR3 to also participate in the RIP-2
to eliminate extra hops
[1] Hedrick, C., "Routing Information Protocol", RFC 1058,
University, June 1988.
[2] Malkin, G., and F. Baker, "RIP Version 2 MIB Extension",
1389, Xylogics, Inc., Advanced Computer Communications,
1993.
[3] Malkin, G., "RIP Version 2 Protocol Analysis", RFC 1387,
Xylogics, Inc., January 1993.
Security
The basic RIP protocol is not a secure protocol. To bring RIP-2
line with more modern routing protocols, an extensible
mechanism has been incorporated into the protocol enhancements.
mechanism is described in sections 3.1 and 4.2.
Author's
Gary Scott
Xylogics, Inc
53 Third
Burlington, MA 01803
Phone: (617) 272-8140
EMail: gmalkin@Xylogics.
Malkin [Page 7]
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