IBM Nortel Networks L2/3, Manual

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Chapter 7. Nortel Networks L2/3 GbESM configuration and network integration
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proprietary Per VLAN Spanning Tree (PVST). An example of this is shown in 7.7, “Advanced
Layer 2 topology sample configurations” on page 80.
Two of the key shortcomings of the original STP standard is that it takes as much as 50
seconds to recover from the failure of a link or device, and that it does not deal well with
multiple VLANs carried over the same physical link (typically by using the 802.1q standard
described above.) These shortcomings are remedied by the 802.1w standard for Rapid
Spanning Tree protocol (RST or RSTP) and by the 802.1s standard for Multiple Spanning
Tree or Multiple Instance Spanning Tree protocol (MSTP or MISTP).
The Spanning Tree functions are configured on the Nortel GbESM with commands from the
/cfg/l2/stg and /cfg/l2/mrst menus.
7.1.4 Routing Information Protocol - RFC1058 and RFC2453
RIP is used by Layer 3 routers to exchange routing table information about the networks
which they can reach and determine how far away are those networks. This facilitates
end-to-end IP connections which traverse multiple routers. Servers can be configured to
listen to RIP information but this is rarely done.
RFC1058 defines the original RIP specification, which was enhanced with the definition of
RIP version 2 (RIP2) in RFC 2453. RIP version 1 has significant shortcomings compared to
RIP2, and therefore RIP1 has largely fallen out of favor. These shortcomings include
limitations on the size of network which can be supported and the completeness of the route
information which can be exchanged using RIP1.
All of the products tested support RIP V2. To configure RIP on the Nortel GbESM, use
commands on the
/cfg/l3/rip menu.
7.1.5 Open Shortest Path First (OSPF) - RFC1257, RFC2328, and others
OSPF, like RIP, is used by Layer 3 routers to exchange routing table information. It is more
scalable and versatile than RIP and recovers from failures more quickly. However, OSPF is
also more complex and more difficult to configure.
OSPF uses a fundamentally different approach to managing routing tables than RIP in that
each router running OSPF maintains a complete representation of the network topology; with
RIP, routers are only aware of their immediate neighbors. As a result of this, OSPF requires
more memory and more processing power than RIP.
All of the products tested support version 2 of OSPF. To configure OSPF on the GbESM, use
commands on the
/cfg/l3/ospf
menu.
Restriction: In our testing, the Cisco implementation of MSTP would only work with other
Cisco products and produced undesirable results when connected to other vendors’
products. The Ethereal
packet decoder was unable to completely decode the BPDUs sent
by the Cisco switches. After our testing was completed, we learned that this is remedied in
IOS version 12.2(25)SEC on the Cisco 3750. We assume that similarly numbered versions
on other platforms will also include this fix.