Migrating from PPP to DHCPo82
jbates at brightok.net
Mon Nov 8 10:36:45 CST 2010
On 11/8/2010 9:40 AM, MKS wrote:
> I work for an small ISP, which does traditional xDSL service with PPPoE.
> Currently we are in the process of migrating most of our customers to
> DHCP (some customers are getting new CPEs and some will be sw upgraded
> remotely ). It would be great if someone has the time to share their
> experience (on- or offline) from such a migration. Common pitfals and
> perhaps what whey would do differently "next time".
> I know that every network is different but I believe that there are
> some general concerns, specially around security of DHCP and security
> features for vendors around DHCP and DHCP snooping etc.
While I'm looking at running option-82 (have limited support in a few
places), I generally run q-in-q providing 100% isolation of customer
ports. This gives me the same protections and tracking that PPPoE or ATM
give me. This also allows me to turn off the security of the DSLAM and
handle all security at the router level.
There are a few deployments we have where q-in-q isn't possible (poor
dslam implementations), and we have utilized dslam security (dhcp
snooping, but currently security breaks IPv6 til the DSLAM gets a future
code update) + option 82 in those cases. A few don't support option-82
or q-in-q, and those generally are static assignments in a CPE.
The only benefit I've ever seen for PPPoE/A is dslam agnostics and
uniform support across all vendors. It has the downside of having to
terminate PPPoE/A on a cpe device. DHCP requires a plan with DLSAM and
Cisco simple (ip unnumbered vlan feature w/ q-in-q, 1 subint per
customer, snmp probe every 5 minutes for the routing table to store
IP->MAC->subint in a database). The only reason I've considered adding
option 82 is to reduce the waste caused by probing (ie, an IP won't
change without the DHCP request, so option 82 lets me get more granular
and not probe).
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