Alcatel-Lucent OmniAccess 5740 - Integrated Routing and Bridging Overview; Alcatel-Lucent Specific IRB Overview

Integrated Routing and Bridging
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OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
Alcatel-Lucent
INTEGRATED ROUTING AND BRIDGING OVERVIEW
When there is a requirement to bridge local traffic within several segments while
having hosts on the bridged segments, to reach the hosts or routers on routed
networks, IRB is configured on the system.
Using this feature, local or unroutable traffic is bridged among bridge interfaces
and routable traffic is routed to other routed interfaces.
IRB allows the user to both route and bridge a protocol in the same router with
connectivity between all the interfaces.
ALCATEL-LUCENT SPECIFIC IRB OVERVIEW
The L2-GE card on the OmniAccess 5740 USG system is a VLAN-aware Ethernet
switch. However, for routing across VLANs or between traffic on the L2-GE card
and other cards such as the T1 or an E1 card, there has to be a mechanism to
detect traffic that is to be routed, and subject it to normal IP packet processing
activities such as filters, NAT, IPsec, FIB lookup, etc. Hence a L2-GE port will then
be capable of taking part in both bridging and routing at the same time. This
technology is called IRB on the OmniAccess 5740 USG.
If the physical ports belonging to a VLAN are thought of as defining a logical
bridge/switch, then the mechanism of sending an incoming packet from this
bridge to the logical router inside the OmniAccess 5740 USG is to connect the
bridge and the router by a logical VLAN interface. This interface forms a logical
pipe between the bridge and the router inside the system. So, the router inside
sees the packet as coming in on a VLAN interface, which behaves like other
interfaces such as Ethernet, Serial, etc., from the point of view of IP services.
Once the packet has undergone the ingress policies configured on the VLAN
interfaces, as well as a FIB lookup, an egress interface is found and the packet is
acted on by the policies configured on this egress interface. If it turns out that the
egress interface is a physical interface such as Ethernet or T1 or an E1 or even a
sub-interface on a physical interface (e.g., a Frame Relay sub-interface), then
everything proceeds as usual. If the egress interface is a logical VLAN interface,
then it will be sent out of the appropriate physical interface port(s) that belong to
the VLAN.