📄 basic rsrb configuration and concepts.htm
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<title>Cisco - Basic RSRB Configurations and Concepts</title>
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<h1>Basic RSRB Configurations and Concepts</h1>
<hr>
<h2>Introduction</h2>
<p>This document will introduce you to RSRB, or Remote
Source-Route Bridging. With Cisco routers, RSRB allows you to
bridge traffic between two Token Rings from separate routers.
First we will talk about creating virtual rings, or ring groups.
Then we'll give you configuration examples for RSRB, using
Direct, FST (Fast Sequenced Transport), and TCP encapsulation,
including some helpful design guidelines. Finally, you'll get a
description of indirect bridging, a technique by which two or
more ring groups can be bridged together. </p>
<p>All the examples given here only show the parts of the
configuration that pertain to the RSRB config. In addition, you
may need to add the command <b>source-bridge spanning</b> to the
Token Ring interfaces to specify how single-route broadcast
traffic should be handled. For more details on how this is
configured, see the document on single-route broadcasts and
Automatic Spanning Tree. </p>
<h2>Virtual Rings</h2>
<p>Virtual rings or ring groups are mechanisms for bridging
together two or more rings. These virtual rings can be extended
between multiple routers, so that all of the rings on multiple
routers are able to communicate with each other. This extension
is done with <b>source-route remote-peer</b> statements. </p>
<p>There are some things to keep in mind when setting up virtual
rings. In order to pass SRB traffic between them, routers must be
part of the same ring-group (virtual ring). Also, routers being
peered together must have <b>source-route remote-peer</b>
statements pointing to each other. For example, picture three
routers (A, B, and C) all in a ring-group. A is peered to B, and
B is peered to C, but A is not peered to C. Routers A and C will
not be able to pass SRB traffic from one to the other, even
though they appear to have a path through router B. The peering
is not commutative. </p>
<h2>Configuration Example - Direct Encapsulation</h2>
<pre>
----------S0 ----------
T0 | |--- | | T0
Token-----|Router A| / |Router B|-----Token
Ring 1 | | ---| | Ring 2
---------- S0----------
// F0
FDDI
F0 //
----------
T1 | |
Token-----|Router C|
Ring 4 | |
----------
|T0
|
Token
Ring 3
</pre>
<p>Direct encapsulation is the simplest type of remote peering.
In order to use direct encapsulation, the routers to be peered
together must be directly attached to each other (i. e. no
intermediate hops) with HDLC- encapsulated serial lines or with
LAN media. When serial lines are slow, or not completely clean,
FST or TCP are better choices for encapsulation types. </p>
<p><b>ROUTER A:</b> </p>
<pre>
source-bridge ring-group 4095
source-bridge remote-peer 4095 interface serial 0
interface serial 0
encapsulation hdlc {default}
interface tokenring 0
source-bridge 1 1 4095 <i>
source-bridge spanning</i> </pre>
<p><b>ROUTER B:</b> </p>
<pre>
source-bridge ring-group 4095
source-bridge remote-peer 4095 interface serial 0
source-bridge remote-peer 4095 interface fddi 0 4000.0000.0003
</pre>
<pre> interface serial 0
encapsulation hdlc {default} </pre>
<pre> interface fddi 0
mac-address 4000.0000.0002 </pre>
<pre> interface tokenring 0
source-bridge 2 1 4095 <i>
source-bridge spanning</i> </pre>
<p><b>ROUTER C:</b> </p>
<pre>
source-bridge ring-group 4095
source-bridge remote-peer 4095 interface fddi 0 4000.0000.0002
</pre>
<pre> interface fddi 0
mac-address 4000.0000.0003 </pre>
<pre> interface tokenring 0
source-bridge 3 1 4095 <i>
source-bridge spanning</i> </pre>
<pre> interface tokenring 1
source-bridge 4 1 4095 <i>
source-bridge spanning</i> </pre>
<p>NOTES: </p>
<ul>
<li>You must use HDLC encapsulation when doing direct
encapsulation over serial lines. If the line is set up
for PPP, X25, or other encapsulation types, direct
encapsulation cannot be used. Since HDLC is the default
encapsulation, this information will not be included in
the configuration file. The router will accept the
command <b>encapsulation hdlc</b> at config time but when
the commands <b>show config</b> or <b>write term</b> are
used, this information will not be displayed. To find
this information, use the command <b>show interface</b>. </li>
<li>Since LANs are multi-access media, MAC Addresses must be
used when doing direct encapsulation over LAN interfaces.
In this case, MAC Addresses were defined for the LAN
interfaces for clarity. However, most of the time, the
burned-in MAC addresses are preferable. To find these
addresses for the FDDI interfaces, use command <b>show
interface fddi x</b>. </li>
<li>An FDDI interface was used here to demonstrate direct
encapsulation over LANs, but it will also work over
Ethernet or Token Ring interfaces. Typically you will not
see direct encapsulation over Token Ring, since local SRB
is usually a better option. </li>
<li>Even though all three routers are part of ring-group
4095, stations on the token ring off of Router A won't be
able to establish sessions with stations on the token
ring off of Router C since these two routers are not
peered together. Router A and Router C cannot be peered
together using direct encapsulation, as there is an
intervening hop (Router B). You can either add a direct
link between Routers A and C and add the appropriate peer
statement, or use one of the other two encapsulation
methods (FST, TCP) to peer routers A and C. </li>
</ul>
<h2>Configuration Example - FST (Fast Sequenced Transport)
Encapsulation</h2>
<p>FST encapsulation's major advantage over direct encapsulation
is that it allows you to extend over multiple hops. However, it
does require a bit more protocol overhead than direct
encapsulation (FST encapsulates SRB packets into an IP packet),
and it relies on a level 3 protocol (IP), while direct
encapsulation only needs level 2 connectivity (HDLC, LAN LLC). </p>
<p>FST introduces a new configuration requirement as well. Each
router using FST peering must have an fst-peername defined. This
name must be an IP address that is in use by an active interface
on the router. The remote-peer statements of routers trying to
access this router must reference the IP address that has been
defined as the fst-peername for the router - using any other IP
address on the box will not work. Use either a loopback interface
or a LAN interface as the fst-peername for stability. </p>
<p><b>ROUTER A</b> </p>
<pre>
source-bridge fst-peername 1.1.1.1
source-bridge ring-group 4095
source-bridge remote-peer 4095 fst 1.2.2.2
source-bridge remote-peer 4095 fst 1.3.3.3
</pre>
<pre> interface serial 0
ip address 1.255.1.1 255.255.0.0 </pre>
<pre> interface tokenring 0
ip address 1.1.1.1 255.255.0.0
source-bridge 1 1 4095 <i>
source-bridge spanning</i> </pre>
<pre> router rip
network 1.0.0.0 </pre>
<p><b>ROUTER B</b> </p>
<pre>
source-bridge fst-peername 1.2.2.2
source-bridge ring-group 4095
source-bridge remote-peer 4095 fst 1.1.1.1
source-bridge remote-peer 4095 fst 1.3.3.3
</pre>
<pre> interface serial 0
ip address 1.255.1.2 255.255.0.0 </pre>
<pre> interface fddi 0
ip address 1.254.1.2 255.255.0.0 </pre>
<pre> interface tokenring 0
ip address 1.2.2.2 255.255.0.0
source-bridge 2 1 4095 <i>
source-bridge spanning</i> </pre>
<pre> router rip
network 1.0.0.0 </pre>
<pre><b>ROUTER C</b> </pre>
<pre>
source-bridge fst-peername 1.3.3.3
source-bridge ring-group 4095
source-bridge remote-peer 4095 fst 1.1.1.1
source-bridge remote-peer 4095 fst 1.2.2.2
</pre>
<pre> interface fddi 0
ip address 1.254.1.1 255.255.0.0 </pre>
<pre> interface tokenring 0
ip address 1.3.3.3 255.255.0.0
source-bridge 3 1 4095
<i> source-bridge spanning</i> </pre>
<pre> interface tokenring 1
source-bridge 4 1 4095 <i>
source-bridge spanning</i> </pre>
<pre> router rip
network 1.0.0.0 </pre>
<p>NOTES: </p>
<ul>
<li>The router RIP statements and IP addresses on serial and
FDDI interfaces show IP connectivity between the routers.
If you can't pass IP traffic between the two IP addresses
used by the peers, FST RSRB won't work. </li>
<li>In this example, the IP addresses of the Token-Ring
interfaces were chosen as the fst-peernames. Any active
IP addresses (for instance, the IP addresses on the
serial or FDDI interfaces) could have been used instead,
as long as the FST peername was referenced consistently
by the peers. For instance, if Router A's fst-peername
statement was modified to read: <b>source-bridge
fst-peername 1.255.1.1</b>, then you would need to
replace <b>source-bridge remote-peer 4095 fst 1.1.1.1</b>
with <b>source-bridge remote-peer 4095 fst 1.255.1.1</b>
on Routers B and C. </li>
<li>Even though there are multiple rings bridged off of
router C, Routers A and B still require only one peer
statement to that router. </li>
</ul>
<h2>Configuration Example - TCP Encapsulation</h2>
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