1.What is the difference between VPN and MPLS?
VPN is generally Virtual Private Network which could be configured by using GRE tunnels.
In that if you want a full mesh than administrator need to setup n*n-1 tunnels. But in case of MPLS VPN, by default CPE works in full mesh form because of route target.
2.What is MPLS and why it is being so popular in short time?
MPLS is multi protocol label switching mechanism which uses the label to forward the traffic to the next hop address.
It is popular because it must be used for CPN (Converge Packet Network).
3.What is the protocol used by MPLS?
MPLS uses TDP or LDP.
4.MPLS works on which layer?
It works between layer 2 and layer 3.
5.What is the difference between P and PE router?
P router doesn’t have Customer network routes where in PE router is having customer network routes.
Another reason is P router doesn’t require MP-iBGP but for PE it is must.
6.Can I make my PE router as P?
To make your PE router as P, you need to remove the BGP configurations and after that it will not participate with customer network.
7.Two routers are having 4 equal cost links, how many ldp sessions will be established?
One session
8.My LDP router id, OSPF router id and BGP router id is different, will it work to forward the traffic of customers or not?
LDP router id and BGP router-id should be same if SP is using labels only for loopbacks. If labels are generated for each and every route then no problem at all.
9.What is Penultimate Hop Popping and why it is required? Which router performs the PHP function?
Second last router performs the Penultimate Hop Popping function to remove the top most label
10.I am receiving aggregate label, what does it mean?
See Aggregate Labels for this answer
11.What are the different types of labels?
one
12.How to make customer route unique?
By adding route distinguisher
ip vrf Customer_A
rd 65000:100
route-target export 65000:100
13.What is the difference between RD and RT?
RD is to define a named vrf while RT is used to share routes between several VRF.
14.Can I assign a same RD to two different customers?
RD is unique and local to router.
15. Is RD travels in route update?
No
16. My customer is having three branches and all are attached to three different PEs, In this case can I use the different vrf names?
Yes
17.What is downstream on demand?
18. How to filter MPLS labels?
By using acl
19. What is the default range of MPLS labels in Cisco routers? How to extend that range?
16 to 100000 is default range
20. Without route reflector can I implement MPLS?
Yes, need to develop full mesh BGP
21. What is the difference between VPNv4 and IPv4 address family?
The answer is so simple, we always accept and forward ip packets to customers, for this we need to use ipv4 address-family. When the customers packets are being received by PE they become labeled one and to forward labeled packets to different PE/RR; address-family vpnv4 is required.
In short we can say that ipv4 address-family is being used for customers and vpnv4 address-family is used by SP core.
22.What is MP-iBGP? Can we use normal BGP in lieu of MP-iBGP?
No, MP-iBGP is used because of the support of multi protocol which normal BGP doesn’t support
23.What is CEF and without enabling CEF, can we make MPLS work?
CEF is mandatory in Cisco routers for MPLS.
24.Iam receiving end to end customer routes on various PE but not able to ping those routes, what’s could be the problem?
LDP is not configured in the path.
25.Does LDP require OSPF, IS-IS or BGP?
IGP is required for IP Reachability
26.In neighbor discovery command, I am receiving only xmit, what does it mean?
At another end MPLS IP is not configured.
27.What is transport address?
Route id is transport address
28.What is the RFC of MPLS?
3031
29.Why MPLS is called multi protocol?
Because it supports almost each and every protocol.
30.What is the difference between MPLS, SSL and IPSec?
I am using different vendor products and want to implement TDP, what type of challenges will you face?
TDP is Cisco proprietary
31. Does MPLS support IPv6?
Yes
32.Can I use the existing IPv4 MPLS backbone for IPv6?
Yes we can use
33. Define various troubleshooting commands in MPLS?
1. sh ip vrf
2. sh ip vrf interfaces
3.sh ip bgp vpnv4 all summary
4sh mpls forwarding-table
5. sh ipcef vrf GBIP
34. What is forward equivalence class aka FEC?
Forward Equivalence Class is used to decide by next hop routing information by routing protocols.
every hop on IGP checks for the external routes in the routing table and forwards the packets correctly.If the no routes are present in routing table then the packets would be dropped. FEC checks each and every steps in tradiotinal routing, which at MPLS VPN case in not possible.
If FEC were being in MPLS also then core routers couldn’t forward the traffic without the knowledge of external routes.
35.If MPLS get disable, will it harm my IGP or IPv4 traffic?
No, IGP will work as it is but MPLS customer traffic forwarding will stop
36. What is MPLS-TP?
MPLS-TP (Transport Profile) is set of protocols which doesn't use any control plane and is defined under IETF. But G-MPLS could be used for the dynamic allocation of labels. MPLS-TP doesn't offer Penultimate Hop Popping and ECMP.
VPN is generally Virtual Private Network which could be configured by using GRE tunnels.
In that if you want a full mesh than administrator need to setup n*n-1 tunnels. But in case of MPLS VPN, by default CPE works in full mesh form because of route target.
2.What is MPLS and why it is being so popular in short time?
MPLS is multi protocol label switching mechanism which uses the label to forward the traffic to the next hop address.
It is popular because it must be used for CPN (Converge Packet Network).
3.What is the protocol used by MPLS?
MPLS uses TDP or LDP.
4.MPLS works on which layer?
It works between layer 2 and layer 3.
5.What is the difference between P and PE router?
P router doesn’t have Customer network routes where in PE router is having customer network routes.
Another reason is P router doesn’t require MP-iBGP but for PE it is must.
6.Can I make my PE router as P?
To make your PE router as P, you need to remove the BGP configurations and after that it will not participate with customer network.
7.Two routers are having 4 equal cost links, how many ldp sessions will be established?
One session
8.My LDP router id, OSPF router id and BGP router id is different, will it work to forward the traffic of customers or not?
LDP router id and BGP router-id should be same if SP is using labels only for loopbacks. If labels are generated for each and every route then no problem at all.
9.What is Penultimate Hop Popping and why it is required? Which router performs the PHP function?
Second last router performs the Penultimate Hop Popping function to remove the top most label
10.I am receiving aggregate label, what does it mean?
See Aggregate Labels for this answer
11.What are the different types of labels?
one
12.How to make customer route unique?
By adding route distinguisher
ip vrf Customer_A
rd 65000:100
route-target export 65000:100
13.What is the difference between RD and RT?
RD is to define a named vrf while RT is used to share routes between several VRF.
14.Can I assign a same RD to two different customers?
RD is unique and local to router.
15. Is RD travels in route update?
No
16. My customer is having three branches and all are attached to three different PEs, In this case can I use the different vrf names?
Yes
17.What is downstream on demand?
18. How to filter MPLS labels?
By using acl
19. What is the default range of MPLS labels in Cisco routers? How to extend that range?
16 to 100000 is default range
20. Without route reflector can I implement MPLS?
Yes, need to develop full mesh BGP
21. What is the difference between VPNv4 and IPv4 address family?
The answer is so simple, we always accept and forward ip packets to customers, for this we need to use ipv4 address-family. When the customers packets are being received by PE they become labeled one and to forward labeled packets to different PE/RR; address-family vpnv4 is required.
In short we can say that ipv4 address-family is being used for customers and vpnv4 address-family is used by SP core.
22.What is MP-iBGP? Can we use normal BGP in lieu of MP-iBGP?
No, MP-iBGP is used because of the support of multi protocol which normal BGP doesn’t support
23.What is CEF and without enabling CEF, can we make MPLS work?
CEF is mandatory in Cisco routers for MPLS.
24.Iam receiving end to end customer routes on various PE but not able to ping those routes, what’s could be the problem?
LDP is not configured in the path.
25.Does LDP require OSPF, IS-IS or BGP?
IGP is required for IP Reachability
26.In neighbor discovery command, I am receiving only xmit, what does it mean?
At another end MPLS IP is not configured.
27.What is transport address?
Route id is transport address
28.What is the RFC of MPLS?
3031
29.Why MPLS is called multi protocol?
Because it supports almost each and every protocol.
30.What is the difference between MPLS, SSL and IPSec?
I am using different vendor products and want to implement TDP, what type of challenges will you face?
TDP is Cisco proprietary
31. Does MPLS support IPv6?
Yes
32.Can I use the existing IPv4 MPLS backbone for IPv6?
Yes we can use
33. Define various troubleshooting commands in MPLS?
1. sh ip vrf
2. sh ip vrf interfaces
3.sh ip bgp vpnv4 all summary
4sh mpls forwarding-table
5. sh ipcef vrf GBIP
34. What is forward equivalence class aka FEC?
Forward Equivalence Class is used to decide by next hop routing information by routing protocols.
every hop on IGP checks for the external routes in the routing table and forwards the packets correctly.If the no routes are present in routing table then the packets would be dropped. FEC checks each and every steps in tradiotinal routing, which at MPLS VPN case in not possible.
If FEC were being in MPLS also then core routers couldn’t forward the traffic without the knowledge of external routes.
35.If MPLS get disable, will it harm my IGP or IPv4 traffic?
No, IGP will work as it is but MPLS customer traffic forwarding will stop
36. What is MPLS-TP?
MPLS-TP (Transport Profile) is set of protocols which doesn't use any control plane and is defined under IETF. But G-MPLS could be used for the dynamic allocation of labels. MPLS-TP doesn't offer Penultimate Hop Popping and ECMP.
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