
Chapter 38 IP Bridge
IES-1248-51V User’s Guide
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Each set of settings is discussed in more detail in the following sections.
38.1.2.1 Domains and VLAN
A domain represents an ISP. Each domain is defined by (and dominates) the VLAN
that are in it and has its own routing table and ARP table. As a result, two or more
VLANs in different domains can use the same IP subnet, and one network can
support multiple ISPs.
VLANs in IP bridges are exclusive. They can be in at most one domain. In addition,
VLANs in IP bridges share the same VLAN space as regular VLANs, so VLANs in IP
bridges must have different VLAN IDs than regular VLANs.
38.1.2.1.1 Configuring VLANs for Domains
To add a VLAN to a domain,
1 Add (Join) a new (undefined) VLAN ID to the domain.
2 Create the VLAN in the system using the regular screens or commands for VLANs.
To remove a VLAN from a domain,
1 Delete the VLAN from the system using the regular screens or commands for
VLANs.
2 Remove (Leave) the VLAN ID from the domain.
38.1.2.2 Edge Routers
Edge routers are usually the gateways that are provided to the subscribers. They
can also be gateways that are specified in static routing table entries. Each edge
router, in addition to its IP address, has an associated VLAN ID. When the IES-
1248-51V forwards a frame to an edge router, it uses this VLAN ID to replace
whatever VLAN ID the subscriber specified. The IES-1248-51V also uses the VLAN
ID to identify the domain the edge router is in.
If two edge routers are in different domains, it is possible for them to have the
same IP address.
38.1.2.3 Downlink Interfaces
Downlink interfaces provide forwarding information for downstream traffic. The
IES-1248-51V learns some of this information by snooping DHCP packets. For
static IP addresses, you should provide this information manually. In this case,
specify the VLAN ID and, optionally, the PVC for a range of IP addresses. The IES-
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