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Author Topic: BRAS IPv4 address  (Read 3090 times)

Weaver

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Re: BRAS IPv4 address
« Reply #45 on: December 11, 2018, 12:17:08 AM »

A very nice concise recap.
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Terrydaktal

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Re: BRAS IPv4 address
« Reply #46 on: December 22, 2018, 09:47:13 AM »

I read that for  IPoE, DHCP option 82 can be used for user authentication based on CVLAN/SVLAN but also IP source guarding I'd imagine? Theoretically the DSLAM could be configured to snoop DHCP handshakes and prevent MAC / IP addr spoofing. I'm not really sure how IP / MAC addr spoofing is mitigated for legacy ADSL2 customers whose data still passes through the MSAN in the exchange and where PPP/L2TP is used, I'd imagine it could be possible for the BRAS to maintain PPPoE session ID - MAC addr bindings and similarly for the ISP gateway to maintain IPCP configured IP addrs - TunnelID/SessionID bindings. Just a intuitive conjecture but I don't know.

Furthermore I assume the DSLAM adds the CVLAN + SVLAN, I assume that a unique QinQ pairing is assigned to each DSLAM port connected to the BRAS and when it arrives at the L2S it switches it to the correct GEA cablelink. Correct me if I'm wrong but that's the most recent mental picture I have.

The bRAS sets up a pseudowire to the ISP gateway (selects ISP based on SVLAN?) over the MPLS backbone and the ISP gateway authenticates based on option 82, 61, something like that.

Finally, does the EEA act as the MSE bRAS and the 21C bRAS at the core node functions as a regular P router?

You said about buzzwords, forgive me, my knowledge of WANs isn't the best.
« Last Edit: December 23, 2018, 08:14:48 AM by Terrydaktal »
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kitz

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Re: BRAS IPv4 address
« Reply #47 on: December 23, 2018, 05:14:59 PM »

I may be totally misunderstanding, because I'm not quite sure where this thread is leading.

>> , I'd imagine it could be possible for the BRAS to maintain PPPoE session ID
>> I'm not really sure how IP / MAC addr spoofing is mitigated for legacy ADSL2 customers whose data still passes through the MSAN in the exchange and where PPP/L2TP is used,


PPP authentication is ISP responsibility and performed by the ISP RADIUS which assigns the IP address.  BTWholesale also use Service Selection Barring on their network to ensure that the EU can only connect to the correct ISP.   There may be times during migration when there is an overlap of 2 ISPs and they used to allow a week or two on both SP domains.

There's an old diagram here for the 20CN network, but there may be a more up to date one on SINET for 21CN

https://kitz.co.uk/adsl/images/l2tpauthentication.gif
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