Re: Diff. Between IP Address Negotiated & DHCP in PPPOE

Hi Everyone,

Just wanted to point out one common misunderstanding about PPPoE IP
address allocation, regarding the command "peer default ip address"

1) When DHCP is used for PPPoE client IP address allocation, the
command "peer default ip address" is NOT required in the server. The
server only has to have matching DHCP pool configured. DHCP reqests
are forwarded as "broadcast" over the PPP link and processed by the
server.

2) If IPCP is to be used for client IP address allocation, the server
must have the command "peer default ip address" specifying a valid
source of IP addresses, e.g. local IP pools or DHCP pools. There are
three main options to "peer default ip address"

2.1) "peer default ip address X.X.X.X" configures the address to be
sent via IPCP manually
2.2) "peer default ip address dhcp" configures the server to query
proxy DHCP server for an IP address. The proxy DHCP server is
configured using the command "ip dhcp-server X.X.X.X". Notice how this
different from DHCP relay: DHCP relay would use the command "ip
helper-address" on the IP interface to forward DHCP packets, while
IPCP translates PPP CONFREQ messages to DHCP messages sent to a remote
server.
2.3) "peer default ip address dhcp-pool <POOL>" queries the local DHCP
address pool for an IP address to be sent to the remote peer.

You may commonly see configurations combining the commands "ip address
dhcp" on the client Dialer interface and "peer default ip address
dhcp-pool NAME" on the server's Virtual-Template. Strictly speaking,
this is not correct: like mentioned above, when using DHCP for PPPoE
client IP address allocation, you dont have to configure the command
"peer default ip address dhcp-pool" in the server - just set up a
matching DHCP pool. In fact, if the *same* pool is used for DHCP and
IPCP, one extra IP address will be requested from the pool by IPCP,
which could have undesirable effects (e.g. if you use address
exclusion). The client will only use the DHCP allocated address.

HTH,

-- 
Petr Lapukhov, petr_at_INE.com
CCIE #16379 (R&S/Security/SP/Voice)
Internetwork Expert, Inc.
http://www.INE.com
2010/4/3 tetooo tetoo <tetoo_me_at_hotmail.com>:
> Dear Joe,
>
> Do you know where can i find PPPOE configuration guide in Cisco DOC-CD,if possible share the link to completely understand that topic.
>
> Thanks
> BR
> Osama
>
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