18. VRF, MPLS & MPLS L3 VPN Flashcards
What is VRF?
Virtual Routing & Forwarding is a technology for creating seperate virutal routers on a single physical routers
What is the difference between VRF and VRF-Lite?
VRF-lite provides VRF without MPLS
Are the VRF instances names CASE sensitive?
Yes
Why must subinterfaces be created with VRFs?
Only one physical interface can belong to a single VRF
What encapsulation must be set on the subinterface?
DOT1Q with a matching VLAN
What is MPLS?
Multiprotocol Label Switching, a packet forwarding method based on labels instead of L3 destination
How does MPLS work upon receiving an unlabeled packet?
The FIB is used to make the forwarding decision. If it indicates the outgoing interface non-MPLS, it will be forwarded unlabeled.
If the interface is MPLS, it will label the packet and forward.
How does MPLS work upon receiving a labeled packet?
The LFIB is used to make the forwarding decision. If it indicates the outgoing interface is non-MPLS, it will remove the packet and forward unlabeled.
If the interface is MPLS, it will forward the packet labeled
What is the LSR in MPLS?
The label switching router
What are the 2 types of LSRs in MPLS?
- Edge LSR
- Intermidiate LSR
What is the LSP in MPLS?
Label Swichted Path, the cumulative unidirectional labeled path that a packet takes through the MPLS domain
Where is the MPLS label placed in a packet?
Between the L2 header and the L3 packet 4-bytes are placed.
Where does the S-bit stand for in a MPLS label?
This indicates if the label is the last label when multiple labels are used in a single packet
What is LDP in MPLS?
Label Distribution Protocol
What is the multicast address used by MPLS?
224.0.0.2
What is the UDP port used by MPLS?
646
What is the TCP port used by MPLS?
646
Which router will become the active router in MPLS?
The router with the higher LDP ID
What is penultimate hop hopping?
The edge LSR advertises a ‘pop’ to neighbor routers to inidcate that he is the border of LSP. Therefore neighbor routers will already remove the label so that the edge LSR can check its FIB, instead of the LFIB
How does a Layer 3 MPLS VPN work?
The customer is connected with a edge LSR of the SP with help of VRF. The edge runs MP-BGP with the other edge LSR. Between them an underlying IGP is used.
How can MP-BGP handle identical customers network prefixes in L3 MPLS VPN?
It uses a ‘route distinguisher’ (RD) that expands the prefix with a unique value per VRF instance basis.
How big is the RD in L3 MPLS VPN?
64-bit that is added to the 32-bit prefix. Together it is called the VPNv4 address
What is the MPLS L3 VPN label stack?
A stack of labels required to forward traffic.
What are the type of labels for the MPLS L3 VPN label stack?
VPN label -
LDP label - to route between Edge LSR
What is the network name for the MPLS domain?
P-network (edge router is called PE)
What is the network name for the customer network in MPLS?
C-network
Which command is used to associcate an interface with VRF?
ip vrf forwarding vrf-name
You have created a VRF instance called RED and associated the required interfaces with it. Which command is used to verify the contect of the VRF routing table?
show ip route VRF RED
What type of router is responsible for adding MPLS labels to a packet?
The ignress LSR
