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Understanding the network.pdf - Back to Home

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interface <strong>to</strong> feed each VLAN, a single high-speed interface can be used with multiple<br />

sub-interfaces. To configure <strong>the</strong> sub-interface on LAN interfaces, use <strong>the</strong> global<br />

configuration command . Here<br />

is <strong>the</strong> Fast E<strong>the</strong>rnet configuration example:<br />

leibniz(config)#interface fa0/0.1<br />

leibniz(config-subif)#ip address 172.16.48.1 255.255.255.0<br />

leibniz(config-subif)#exit<br />

leibniz(config)#interface fa0/0.2<br />

leibniz(config-subif)#ip address 172.16.49.1 255.255.255.0<br />

leibniz(config-subif)#exit<br />

leibniz(config)#interface fa0/0.3<br />

leibniz(config-subif)#ip address 172.16.100.1 255.255.255.0<br />

leibniz(config-subif)#exit<br />

leibniz(config)#interface fa0/0.4<br />

leibniz(config-subif)#ip address 172.16.32.1 255.255.255.0<br />

leibniz(config-subif)#exit<br />

With certain FR <strong>to</strong>pology implementations utilizing sub-interfaces with FR, along<br />

with <strong>the</strong> Layer 3 addressing and DCLI information, some additional interface<br />

configuration options might be required. The first of which might be <strong>the</strong><br />

configuration of an FR map. FR maps are needed if inverse ARP (Layer 3 address <strong>to</strong><br />

DCLI mapping, which is enabled by default) is disabled or not supported by <strong>the</strong><br />

Layer 3 pro<strong>to</strong>col being implemented. In <strong>the</strong>se cases, <strong>the</strong> mapping needs <strong>to</strong> be done<br />

in order for <strong>the</strong> <strong>network</strong> traffic <strong>to</strong> be transmited over <strong>the</strong> correct VC. In <strong>the</strong> previous<br />

configuration example, FR maps are used <strong>to</strong> associate different AppleTalk <strong>network</strong>s<br />

with specific sub-interfaces.<br />

The second option allows you <strong>to</strong> specify whe<strong>the</strong>r or not <strong>the</strong> interface will function as<br />

a FR point-<strong>to</strong>-point or FR multipoint interface (<strong>the</strong>re is no default). The<br />

point-<strong>to</strong>-point designation is used when a sub-interface has a single DCLI.<br />

Multipoint designation is used when multiple DCLIs are associated with <strong>the</strong><br />

sub-interface, or if <strong>the</strong> FR provider is providing multipoint grouping.<br />

By using <strong>the</strong> "multipoint" designation, you are instructing <strong>the</strong> router that all <strong>the</strong><br />

associated DCLIs are allowed <strong>to</strong> exchange frames (using inverse ARP or frame-relay<br />

maps <strong>to</strong> handle <strong>the</strong> DLCI <strong>to</strong> Layer 3 address mapping). This distinction is what<br />

makes it possible for one router <strong>to</strong> function as a multipoint hub in<br />

point-<strong>to</strong>-multipoint <strong>to</strong>pology implementations where <strong>the</strong> multipoint router has<br />

point-<strong>to</strong>-point PVCs <strong>to</strong> two or more endpoints. These single endpoints <strong>the</strong>n<br />

exchange packets with each o<strong>the</strong>r through <strong>the</strong> multipoint router. However, although

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