Unformatted text preview: different subnet The routing table at the source host should contain the IP The address of the router, say 220.127.116.11 in this example, for handling packets for different subnet, e.g. a default gateway In ARP table at source, ﬁnd MAC address E6-E9-00-17-BB-4B, In for this IP address 18.104.22.168 of the router o.w. ARP for it Hubs, Bridges and Switches
Used for extending LANs in terms of geographical coverage, Used number of nodes, administration capabilities, etc. Differ in regards to: Differ
collision domain isolation collision Layer in the protocol stack at which they operate Layer Hubs
Physical Layer devices: essentially repeaters operating at bit Physical levels: repeat received bits on one interface to all other interfaces Hubs can be arranged in a hierarchy (or multi-tier design), with Hubs multi-tier a backbone hub at its top backbone hub Each connected LAN is referred to as a LAN segment Each segment Hubs do not isolate collision domains: a node may collide with Hubs do collision any node residing at any segment in the LAN Hubs (Cont d)
Hub Advantages: Hub
+ Simple, inexpensive device + Multi-tier provides graceful degradation: portions of the LAN continue to operate if one of the hubs malfunction +Extends maximum distance between node pairs (100m per Hub) Hub Limitations: Hub
- Single collision domain results in no increase in max throughput; the multi-tier throughput same as the the single segment throughput - Individual LAN restrictions pose limits on the number of nodes in the same collision domain (thus, per Hub); and on the total allowed geographical coverage - Cannot connect different Ethernet types (eg 10BaseT and 100baseT) Bridges
Link layer device Link stores and forwards Ethernet frames stores examines frame header and selectively forwards frame based on examines MAC dest address when frame is to be forwarded on segment, uses CSMA/CD to when access segment transparent transparent hosts are unaware of presence of bridges hosts plug-and-play, self-learning plug-and-play, bridges do not need to be conﬁgured bridges Bridges: trafﬁc isolation
Bridge installation breaks LAN into LAN segments Bridge bridges ﬁlter packets: bridges same-LAN-segment frames not usually forwarded onto other LAN same-LAN-segment segments segments become separate collision domains segments collision domain bridge collision domain = hub = hos...
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This note was uploaded on 12/08/2010 for the course IEG IEG3310 taught by Professor Wingc.lau during the Spring '10 term at CUHK.
- Spring '10