1. Host and Small Network Relaying Howard C. Berkowitz
Chapter 6
Host and Small Network Relaying
Howard C. Berkowitz
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

2. Host and Small Network Relaying
Hosts can be passively aware of routing
Simple default gateway
More complex load sharing
Can also act as routers
Relay packets from host to host, or external routers.
Relaying general concept that involves switching and routing.
RIP-simple signaling mechanism for hosts to find the default gateway.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

3. Workgroup Switching Switches
Good tool to provide fast paths to local servers
Reduce latency
Network designer goal is to provide useful bandwidth.
Do not want to provide more bandwidth than a server can use.
Server should be free from waits for bandwidth, it should be full dup and Gb range.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

4. Workgroup Switching Reasons to use switches VLANs
Min bandwidth contention on servers
100mbps and full dup
Provide fast inter-host paths when there is significant peer-to-peer operation.
VLANs
Broadcast and multicast isolation
Some automation of moves and changes
Cabling flexibility
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

6. Alternatives to Routers for Inter-subnet Communications
Application Gateways
Hosts do not need to communicate with one another
Communicate with servers
Application gateways are ideal in an office automation setting
Products can have firewall as well as router functions.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

7. Shared Access to Printer and a WAN Gateway.
Cached Access to a Printer and a WAN Gateway
Lookups normally sent to data center can be done on a local cache
Small switch could be useful for speeding access to critical cache servers.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

10. Local Mail Gateway
Switch allows concurrent transfers between one client and the cache.
Other client transfers to external gateway and the printer.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

12. Alternatives to Routers for Inter-subnet Communications
Multiple Interface Servers
Connect a server to multiple use LANs and interfaces.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

13. Alternatives to Routers for Inter-subnet Communications
VLAN-Aware Servers
Multiple interface method to bring VLANs into the server.
VLAN aware server card
Server will appear to be on each VLAN
No router required
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

14. Hosts’ Involvement in Routing
Basic Router Location
Host must be able to find default gateway.
Hard-Coded Default GW
Proxy Address Resolution Protocol (ARP)
Router Discover protocols IDRP
Passive RIP-simply to find default gateway
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

15. Hosts’ Involvement in Routing
Passive RIP For Router Location and other functions
RIP often runs on non-routing hosts
Done to find default gateway
Load Sharing-spreads load over shared resources
Load balancing-uses more overhead
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

16. Hosts’ Involvement in Routing
Interactions with Microsoft RAS
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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

19. RIP Workload and Convergence
RIP Traffic
Oldest protocol that is still used
Convergence Time
Only keep track of routes that it is currently using.
Sum of basic failure detection and the time to get an update.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

20. When and How to Use Routing in Small Networks
RIP is a simple choice for many networks-not always the best choice.
Static routing could be a better choice.
RIP is adequate for router discovery and very simple topologies.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

21. When and How to Use Routing in Small Networks
Hub-and-Spoke Topology
All servers at the data center
Spoke sites only need to know how to reach the data center.
Overhead
For small networks overhead for RIP is minimal
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

23. When and How to Use Routing in Small Networks
Distributed Topology with Equal Cost Paths
Quasi-static routing can be practical when dealing with a few nodes
More complex topologies need dynamic routing
A single alternate path almost always increases availability.
The more alternate path topology approaches full mesh, the more overhead it takes to converge.
Holddown timer keeps being reset.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

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Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

25. When and How to Use Routing in Small Networks
Distributed Topology with Unequal Cost Paths
RIP is unaware of bandwidth on links.
Only minimizes the number of links taken.
OSPF or EIGRP works well
Static can work if topology is not to complex.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing

26. RIP Version 2 Added features but did not change limitations of RIPv1
VLSM and CIDR
Send updates as multicasts rather than broadcasts.
7/15/2019
Designing Routing and Switching Architectures. Copyright 1999 Macmillan Technical Publishing