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New Member

Load Balance traffic between BRAS routers ?

Hi all ,

ISP environment with 3 Cisco 7200 BRAS ( NPE-G2 ) , we need to load balance traffic between two of them so the load balancer will accept traffic from backhauling link and distribute traffic the upper two BRAS , can we achieve this using spare 7200 we have or is there any software solution can do this .

another question , Cisco 7200 VXR ( NPE-G2 ) , does it support concurrent calls or sessions from more than 16000 subscriber ??

thnx ,

Everyone's tags (1)
13 REPLIES

Re: Load Balance traffic between BRAS routers ?

Hi Shadi AbuJubba

Coming to the Second Question First...Could not find much info on the Session Capacity from my search for Online Cisco Documentation...It defintely says more than NPE-G1( >8000 ) but not an exact figure...Cisco 10K has upto 32K Limit...May be your Cisco Account Rep can help you on eaxct details if you are lucky to have one or someone else around here will give you a hand

http://www.cisco.com/en/US/prod/collateral/routers/ps341/prod_bulletin0900aecd8047188c.html

Coming to first question second when we say to load-balance across BRAS do we have a Service-Based VLAN Model for transporting the Subscriber PPPoE sessions to BRAS (Hope we are talking for Load-Balancing of IP DSLAM traffic ) ?

What is the Backhauling Transport Network being used to connect the DSLAMs to the BRAS on Layer 2 ie MPLS L2VPN or P2P Ethernet Links aggregating to an Ethernet Switch before terminating on the BRAS ?

Regards

Varma

Re: Load Balance traffic between BRAS routers ?

Hi Shadi,

just my thoughts here

Lets assume you have 3x 7200 routers. R1, R2 , R3.  R1 and R2 are the upstream routers and R3 is the sort of router where your backhaul from DSLAMs come in could be Ethernet backhaul or an ATM backbone.( hoping that we are talking about load balacncing the customer PPP sessions)

1. If you have ATM backbone then you could use R3 as a LAC and R1 and R2 as LNS and have L2TP between R3-R1 and R3-R2 and the PPP will terminate on R1 and R2. You can split the vpdn-groups for customer and have the virtual termplates confgured on the upstream routers in a 50-50 or whatever percentage you want. Thats how most SP's would split their customers having multiple BRAS' per POP.

2. If you are running Ethenet backhaul then you can split your vlans carrung PPPoE traffic but that would mean that you need some switchin infrastructure in place already.

Hope this gives some sort of an idea. I could be corrected here by other experts.

Regards,

Kishore

New Member

Re: Load Balance traffic between BRAS routers ?

hi Kishore ,

thanks for your reply .. kindly review my reply to varma to understand our setup and i hope this will be clear to you .

Regards,

New Member

Re: Load Balance traffic between BRAS routers ?

Hi varma ,

first thanks for replying ...

for the second question , as per my readings NPE-G1 is supporting 16k session and NPE-400 support 8k session and based on that NPE-G2 should support 32k sessions which confuse me because in this case i can save money anu use 7200 VXR with NPE-G2 rather than purchase 10k , right ??!! .

for the first question , I really do not know the exact topology because it is my first week and I am new to ISP industry , but inside our POP we have this topology ,

3 BRAS 7200 working as LNS and each BRAS has bachhaul from teleco ( Fiber connection ) , each BRAS is connected to central L3 4500 switch , OSPF is runing beween BRAS and L3 SW , each BRAS is located in OSPF area for summarization purposes which means 3 BRAS and 3 areas , L3 SW is the backbone area . then L3 SW is connected to 2 SCE 2000 for traffic optimization and finally the SCE 2000 is connected to Gateway router 7200 to ( running BGP ) .

our DSL is based on PPPoE and of course L2TP .

so based on the above what type of backhauling you think we have and what is your recommendation for load balancing ??

big thanks ,

shadi

Re: Load Balance traffic between BRAS routers ?

Hi Shadi

Again second question first Totally agree with you if c7200-VXR with NPE-G2 can provide the same Scalbility as c10k in terms of number of sessions as well as operating performance with the traffic load it won't be a better call to go for a 10k indeed. Unfortunately I could not get much of online support documentation available for the NPE-G2 session capacity available .. I would advise you before deciding on the dimensioning of the session capacity over each BRAS please get support from Cisco if your products are under support contract and do not do any dimensioning on assumptions as this might have a remarakable impact in the live environment.

Now coming back to the first question second

What you have described in above post  is the Uplink L3 connectivity from BRAS towards Internet Gateway and is not related anyway to design challenge you are dealing with for subscriber session load-balancing among BRAS...We should not worry for that as this point of time...The aim is to load-balance the DSL Subscribers PPPoE sessions among the BRAS available..Now since this is an IP DSLAM Traffic and you have mentioned that Each BRAS has fiber backhaul from Telco so I would like to mention that the possible ways to uplink DSLAM Traffic to BRAS are:

1. DSLAMs traffic has to be aggregated first on a downstream aggregation Switch and then that Switch will be uplinked to BRAS carrying the Service VLANs

2.If MPLS L2VPN is the transport then individual DSLAMs can be assigned a VLAN per service which is Per Service Per DSLAM Model and then we have the choice to uplink it to respective BRAS.

DSLAMs can not directly be backhauled to BRAS as the BRAS ports are very expensive and so we aggregate the DSLAM Traffic before terminating on the BRAS

Actually here the requirement is to load-balance the L2 PPPoE sessions among BRAS available and the only option to my best understadning is to load-share the customer sessions across respective BRAS but we can not load-balance...To put simple its as easy as we have multiple GWRTRs in our LAN and its our choice which VLAN we terminate on which GWRTR...We can not terminate same VLAN on two GWRTR except HSRP and I have not seen any HSRP for DSL PPPoE Sessions yet....Hope you are getting my point...

My suggestion would be first go through and understand the Backhaul Network Topology currently in place from architectural point of view and then decide the most optimum load-sharing among the BRAS..

Hope this provides some insight in your current traffic requirement.

Regards

Varma

New Member

Re: Load Balance traffic between BRAS routers ?

hi again varma ,

I am really appreciating your replies ... I got your ideas boss and i will be back to discuss after getting the whole picture but for the moment i want to ask , if i have only 3 backhauling lines coming from teleco and 4 BRASs , how i can feed one backhauling to two BRASs .. let say plug it to L3 switch ( specific VLAN ) and out two links to BRASs ?

thnx ,

Re: Load Balance traffic between BRAS routers ?

Hi Shadi

BRAS is the point of termination for the Customer DSL PPPoE Sessions and becomes the first L3 Hop for the Subscriber and hence we can not put any L3 Switch before BRAS but only L2 Switch and as said above for the L2 Sessions we can only load-share not load-balance..If we have only 3 lines coming from Telco and assuming eac of them to be Ethernet Trunk Link and we are having per DSLAM per Service VLAN Model we can place an L2 Switch before the 4 BRAS and uplink 4 Ethernet Links to each BRAS splitting the VLANs accordingly per our choice...The Telco Lines here terminate on the L2 Switch and noton the  BRAS..

Hope this helps to answer your question.

Regards

Varma

Re: Load Balance traffic between BRAS routers ?

Shadi,

If your case is where your telco is sending the PPP sessions via  Ethernet. you have a choice of either using either bba groups or vpdn. You can have L3 switch in between thats not an issue but please remember that the PPP sessions will terminate on the BRAS. Now if you will be terminating them on your BRAS.

LNS1:
 bba-group pppoe global
  virtual-template 2
 LNS2:
 vpdn-group pppoe
  accept-dialin
   protocol pppoe
   virtual-template 2

As I mentioned you can split the customers on vlans. The vlans terminate on the BRAS's. You can send setup trunks and allow specific vlans to terminate on the BRAS"s please find below a topolog that I have drawn for you. Hope that give you some idea.The vlans dont have to be same number as they will be Q-in-Q  between your downstream telco and your switch. Hope this gives some idea

Re: Load Balance traffic between BRAS routers ?

Hey Kishore

I got little confused with your statement of using L3 Switch between Customer and BRAS

How is that placed as an L3 element in the DSL Network topology between DSLAM and BRAS or do you mean to say we can place and L3 Switch but it will do L2 functionality only..

Regards

Varma

Re: Load Balance traffic between BRAS routers ?

Hi Varma,

How is that placed as an L3 element in the DSL Network topology between DSLAM and BRAS or do you mean to say we can place and L3 Switch but it will do L2 functionality only..

Yep thats right. You can place a L3 switch which can function as an aggregate switch for other L3 scenarios. But for this scenario it will ony act as a L2 switch to ship the PPPoE frames across. Sorry I thought I mentioned it but i didnt.

Regards

Kishore

New Member

Re: Load Balance traffic between BRAS routers ?

Guys I am very thankful to your replies and I am sorry for late in thanks ....

I have question , regardings the design i mentioned in our NW , our BRAS is working as LNS right ?

if Yes and i expect it is Yes , then the LAC is locating in the Telecom side and actually what we recieve is not PPPoE session as it encapsulated inside L2TP tunnel , based on that on what ratio or how many PPPoE session is encapsulated inside L2TP tunnel and when we say NPE-G2 is able to recieve let say 16k session , does that mean 16k L2TP sessions or PPPoE sessions ?

the second question , what is the idea PPPoE encapsulated inside L2TP between LAC and LNS , for what we need this encapsulation , why not leave the PPPoE session pass to LNS as all traffic still in L2 ??

Regards,

Shadi

Re: Load Balance traffic between BRAS routers ?

Hi shadi,

.....how many PPPoE session is encapsulated inside L2TP tunnel and when we say NPE-G2 is able to recieve let say 16k session , does that mean 16k L2TP sessions or PPPoE sessions ?

IMHO the L2TP tunnel can contain as many sessions based on the platform. Obvioulsy there is a limitation of the number of PPPoE session. No, it doesnt mean 16k L2TP sessions. It means 16k PPPoE sessions.One L2TP session can handle hundred's of PPPoE sessions and you can limit them as well as how many you want per L2TP session.

Normally upstream Telco's have multiple L2TP tunnels for redundancy.

the second question , what is the idea PPPoE encapsulated inside L2TP between LAC and LNS , for what we need this encapsulation ,

You need encapsulation as you are using a different protocol for transportation.

 why not leave the PPPoE session pass to LNS as all traffic still in L2 ??

Well , how does you telecom know which PPP sessions to direct to you if it jsut transports all of the PPP sessions to you. That means it might end up sending other customers PPP sessions to you as well right?

LAC works more of a aggregator. What it does is to check the PPP sessions coming from the  subscribers and see which LNS it needs to go to based on the domain.and then bundles them all together and sends them off the correct LNS thru the tunnel.

for eg: if your DSL modem is sending  test@xyz.com as the  CHAP username then the LAC identifies the domain as @xyz.com and sends it off to which ever ISP it needs to go to.

Hope this gives you an idea.

Regards

Kishore

New Member

Re: Load Balance traffic between BRAS routers ?

Hi again Varma ,

Kishore Chennupati wrote:

You need encapsulation as you are using a different protocol for transportation

could you please explain more what different protocols is using ?

Kishore Chennupati wrote:

Well , how does you telecom know which PPP sessions to direct to you if it jsut transports all of the PPP sessions to you. That means it might end up sending other customers PPP sessions to you as well right?

LAC works more of a aggregator. What it does is to check the PPP sessions coming from the  subscribers and see which LNS it needs to go to based on the domain.and then bundles them all together and sends them off the correct LNS thru the tunnel.

for eg: if your DSL modem is sending  test@xyz.com as the  CHAP username then the LAC identifies the domain as @xyz.com and sends it off to which ever ISP it needs to go to.

Hope this gives you an idea.

Regards

Kishore


I understand that LAC is doing lookup based on domain name to forward the PPP traffic to specific ISP , but why not do it one by one , means LAC got PPP session then determine the destination ISP and forward this session to ISP LNS ( working as multiplexer in this case ) rather than adding overhead by collect PPP sessions and create L2TP tunnel then transport within L2TP tunnel , don't think this take time ( latency ) and add extra payload to frame ( overhead ) ?

sorry my questions is lot but i need to understand the process deeply !! thanks very much for your time and advices

Regards ,

Shadi

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