Thursday, January 28, 2016

What is Virtual Network Function or VNF?

In a Network Functions Virtualization(NFV) architecture, a virtualized network function, or VNF, is responsible for handling specific network functions that run in one or more virtual machines on top of the COTS hardware. In a virtualized environment, a virtual network function means that a company has taken the software that actually performs a specific function, abstracted it from their own hardware, and packaged it to run on any standard server.

The primary goal for NFV is to decouple software implementations of network functions from the compute, storage, and networking resources in the network. The software that performs the specific network function is generally called Virtual Network Function aka VNF. Examples of VNFs are P-Gty, GGSN, Session Border Controller and Virtual Router. When a function of ROUTER or UTM is virtualized it is called VNF. When we club all the sub functions of VNF into one it become virtual ROUTER or virtual UTM.
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Thursday, July 16, 2015

Segment Routing Based MPLS Vs Classic MPLS

Previous post has already covered why segment routing is required with all it's basic information. This post is mainly focusing on difference between SR Based MPLS Networks Vs Classic MPLS Networks.
Segment Routing Based MPLSClassic MPLS
IGP/LDP synchronizationNot RequiredRequired and Added More Latecny in Convergence
Extra TE states to support FRRNo extra stateExtra states to manage
Optimum backup pathYesNo
ECMP-capability for TEInbuiltNo
TE state only at headendYesNo (n^2 problem at midpoint)
Seamless Interworking with classic MPLSYesNA
SDN SupportYesNo
RoutingConstraint Based (Source can Define)Destination Based + RSVP-TE
Link information (Bandwidth, IGP metric, TE metric, SRLG ) is flooded throughout the IGP domainNo
Path CalculationCSPF or By Using Centralized ControllerIGP + RSVP-TE
Operations and TroubleshootingLowHigh
And here is the rest of it.
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Monday, July 13, 2015

Layer 3 MPLS VPN with Segment Routing - Nodal Segment

Traditionally Layer 3 MPLSVPN service requires two labels; VPNv4 Label and LDP (Transport Label). LDP is used to distribute the transport labels within service provider domain. But let’s see how Layer 3 MPLSVPN service will work in case of Segment Routing.

Below is the topology which has configured IGP and MP-iBGP for Service Provider network. CE1 and CE2 are two sites of same customer which are part of same vrf. This service provider core is free from LDP.

Segment Routing is used for transport label however MP-iBGP is used for VPNv4 labels. On every SR capable router, Loopback interface is configured as Node segment ID which is also called as Prefix segment ID.

Label 200 is Node/Prefix SID of PE2 and is advertised in the IGP protocol as SR label which is part of SRGB. For PE1 reaching CE2; BGP next hop is a PE2 loopback. PE2 loopback is flooded as a label of 200 in the IS-IS sub-TLV extension or OSPF Opaque LSA.

PE1 pushes label 200 as transport label and 500 as inner label.
PE1 and P1 don’t change the transport label and send the packet to the P2. P2 receives an implicit null label for the loopback of PE2, P2 does PHP (Penultimate Hop Popping), and thus only the VPN label is sent to the PE2.

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