agent, the DHCP relay agent inserts the sub options of DHCP Option 82, such as subnet selection and VPN
ID options. These options are considered by DHCP server while allocating IP address.
DHCP clients use the L2 AC interface to access EVPN bridge domain and use BVI interface as default gateway.
So the clients must get the IP addresses from the DHCP server as in the same subnet of BVI interface.
DHCP Request Forwarding Path
Clients broadcast requests to the access switch with DHAA to EVPN PE routers. The access switch does load
balancing. The load balancing configurations in access switch will impact PE in DH-AA and DHCP to send
the DHCP requests. The DHCP request reaches the Bridge Domain (BD) BVI interface which is configured
with DHCP relay. Because AA PE routers are configured the same IP addresses, BVI IP addresses cannot be
used as DHCP relay source IP address.
For DHCPv4, configuring GIADDR field for each DHCP relay profile is allowed. Loopback interface with
unique IP addresses can be configured in VRF which is reachable to DHCP servers. Configuring DHCP relay
source address is not supported.
In case of DHCPv6 servers, DHCPv6 relay picks up an available Loopback interface IPv6 address as DHCPv6
relay source IP address. After the DHCP clients get the IP address. DHCP clients are not normally routable
to DHCP servers. DHCP clients send unicast DHCP renew messages to the DHCP server. If the DHCP servers
are not routable, the DHCP unicast messages fail, then the DHCP client sends broadcast rebinding messages
with the corrsponding DHCP relay.
In the below figure, DHCP clients are configured on PE11 and PE12.
Figure 85: EVPN IRB with ASR 9000 as Centralized DCI Gateway
Configuration
Perform the following tasks to configure the EVPN IRB: DHCPv4 and DHCPv6 Relay feature:
/* PE11 configuration */
Router# dhcp ipv4
Router(config-dhcpv4)# profile DHCPv4_RELAY relay
Router(config-dhcpv4-relay-profile)# helper-address vrf default 10.20.20.20 giaddr 192.0.2.1
Router(config-dhcpv4-relay-profile)# relay information option vpn
Router(config-dhcpv4-relay-profile)# relay information option vpn-mode rfc
Router(config-dhcpv4-relay-profile)# exit
Router(config-dhcpv4)# exit
Router(config)# interface BVI1 relay profile DHCPv4_RELAY
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
613
Configure EVPN IRB
Configuration
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