[c-nsp] 7609 DHCP alternatives - EVC / Subinterfaces

[Victor Lyapunov]

Hi All

I am trying to test DHCP functionality with 7600 router. Traffic
arrives from all customer facing interfaces (ES+), arrive using the
same VLAN. 7600 perfoms DHCP relay and acts as a gateway for all of
them. With the new cards ES+ we have two options for the configuration
of customer facing interfaces

1. Using EVC + SVI interface

  int g4/1
     service instance 100 ethernet
     encapsulation dot1q 100
     rewrite ingress tag pop 1 symmetric
     bridge-domain 100 split-horizon
  int g4/2
     service instance 100 ethernet
     encapsulation dot1q 100
     rewrite ingress tag pop 1 symmetric
     bridge-domain 100 split-horizon

  int Vlan 100
     ip address 10.0.0.1 255.255.255.0
     ip helper address 192.168.0.1

2. Using IP subinterfaces

  int loopback 100
     ip address 10.0.0.1 255.255.255.0

  int g4/1.100
     encapsulation dot1q 100
     ip address unnumbered loopback 100
     ip helper address 192.168.0.1

  int g4/2.100
     encapsulation dot1q 100
     ip address unnumbered loopback 100
     ip helper address 192.168.0.1


Both configurations seem to achieve the same effect but I am not sure which one
is the preferable for large amount of traffic / subscribers.

For example due to the bridge domain I would expect that the first
alternative will
create more entries in the mac-address table.

Thanx

Victor