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1. WAN DHCP setup 2. WAN PPPoE setup

Kyujin Choi
Level 1
Level 1

Question1 (WAN DHCP IP)


  We have multile branch offices connected through IPsec tunnel at HQ

  When I looked at ASA tunnel information, IPsec tunnel has been established through public IP of branch offices. (i.e

  There are two branch offies using DHCP (not Static IP from ISP). They are also connected through IPsec tunnel through public IP address.

  What if ISP changes ip address of WAN interface of CE (our router?) because of DHCP lease timer.

   It seems like that we didn't have any issue so far (more than 2 year) in terms of IPsec tunnel.

  Is there any contract that between ISP and customer can have in order to get a same IP address even if DHCP is enabled? (I know technically how to assign same ip address from router, but i do not have any exprience whether ISP can do this in terms of policy)

Question 2 (PPPoE DHCP)

almost same situation as quesiton 1.  WAN ip address never changed even if wan interface is set by DHCP. anyhow 2nd question is little different from question 1. When wan interface is set by PPPoE, what kind of information that I need from ISP? Things that I know are mtu size (1492) encapsulation ppp, pppoe enable at WAN interface of CE, ppp hostname / password. what else did i miss?

PE----- Modem/Router (bridge mode) --- CE (cisco router)

I couldn't see ISP router setup, but I guess there may be like below

interface sx/x

mtu 1492

peer default ip address pool xxxx  (DHCP range)

ppp authentication chap (chap or pap)

ip local pool xxxx y.y.y.y (DHCP range)

Client router

interface f0/4

mtu 1492

encapsulation ppp

pppoe enable

ppp chap hostname xxxx

ppp chap password xxxx

Question 3.  when WAN interface got a IP address through PPPoE, gateway is not same subnet. Can anybody explain this?




1 Reply 1

Answer 1: You can just set your vpn tunnel by configuring dynamic-to-static vpn, so you don't need to worry about dhcp assignment on your branch's side.

Answer 2: you need to know only what you mentioned to setup a pppoe connection.

Answer 3: I think when your connection is p-to-p it is not necessary that the gateway has to be on the same subnet, sometimes you can configure it on another subnet.

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