HI ALL , Thanks for overwhelming and valuable information , now I understand the benefit on QoS group anywhere and used on P router and that to group traffic with EXP-2 and EXP-3 and treat both of them with the same policy on the output interface , so I think it is useful in real life network , but in case of CCIE SP LAB it is mostly used on the PE router as you said Actually I am going for lab exam on august and I don’t have enough time for mysteries L Hisham , I have observed that you got CCIE SP congratulation J , hope to hear from you to benefit from your experience on the exam Appreciate if we can stay connected offline , this my MSN … anyone interested please add me [EMAIL PROTECTED] Mohamed Hamed Network Consulting Engineer Mobile (KSA-Riyadh): +966543464502
Date: Wed, 25 Jun 2008 04:04:58 +0530From: [EMAIL PROTECTED]: [EMAIL PROTECTED]: Re: [OSL | CCIE_SP] QoS groupYeah Hisham,Thanks for a nice explanation,That's quite correctly said, Always the values from the IP precedence field are propagated through the labels stacks during the label imposition (case of an MPLS-PE ingress router). EXP values never propagated to the newly exposed label during the POP operation. <<< use QOS-GRP/Explicit-Null here Whenever we need to make decision on the exit interface based on incoming MPLS label which is popped as per the current forwarding-table <<< use QOS-GRPMostly we @ ingress set the label imposition stack, iff we set the topmost only then again we will have to take care of the popping operation and the EXP value.Using Explicit-Null achieves the purpose of exp value retention as the Null value is used to carry the EXP bits. and we don't have to worry about the qos-grp usage.Thanks,Dara On Wed, Jun 25, 2008 at 2:07 AM, hehsam elezaby <[EMAIL PROTECTED]> wrote: Hello , I would like to add a piece of info which helped me so much during my lab preparation and made me understand MPLS QoS scenarios very well.*** The EXP field is copied from whatever there is below it during label imposition. For example if we have an ingress PE and it is doing MPLS VPN label imposition , it will apply same value as IP Precedence to both MPLS labels being added on top of the IP packet.*** The opposite is not correct i.e During label disposition (popping) the EXP value is not copied to whatever is below it. The label will be popped and nothing will be propagated downwards.We always need QoS groups on PE routers when we do policies in the egress direction to the CE based upon provider markings (EXP bits). The packet arrives at the PE with only the VPN label and it copies the EXP value into the QoS group and then performs egress policy based on whatever value is inside the QoS group. This is what we usually call the "pipe mode". You will never need such a setup if the customer packet already has DSCP or IP Precedence marking because we will be simply doing our policy based on the original customer marking AKA "short pipe" mode.But what is for some kind of reason (usually a forced marking policy configured in the middle of the provider network) the MPLS VPN packet will have different EXP values on both labels and the PHP router (P router one hop before PE) will then pop the topmost label and propagate the packet with an unrealistic label i.e bottom label which should have been changed too but it actually didn't (again as i explained in the second point , the EXP value will never be propagated in a pop operation). We need to guarantee that the policy is based upon the topmost label EXP value so we copy it into the QoS group on the PHP router and then perform policy based on this value in egress direction to PE router. This could be needed in both "pipe" and "short pipe" modes because it is something related to the P router and not the PE.Finally , if we have Explicit null enabled , we will never need any QoS groups on the P routers because it will always be sending a dual stack label to the PE router no matter what happens. But definitely we will still need it on PE routers in egress policies as i explained before for the "pipe mode".I hope this helps.Hisham El-EzabyCCIE# 21190 (SP) ----- Original Message ----From: mohamed hamed <[EMAIL PROTECTED]>To: OSL CCIE Service Provider Lab Exam <[email protected]>Sent: Monday, June 23, 2008 11:35:54 PMSubject: [OSL | CCIE_SP] QoS group Hi everyone, Does anyone know where we should use the QoS group on P or PE Router? As I understand that we usually use it on PE router, but I found some Labs on the internetwork expert use it on P router as well If anyone knows why we should use QoS grouo on P routers , please unicast me a mail back Mohamed Hamed Network Consulting Engineer Mobile (KSA-Riyadh): +966543464502 Introducing Live Search cashback . It's search that pays you back! Try it Now _________________________________________________________________ The other season of giving begins 6/24/08. Check out the i’m Talkathon. http://www.imtalkathon.com?source=TXT_EML_WLH_SeasonOfGiving
