New-generation Protocols 99
opposed to the convention 6 bytes occupied by the Ethernet frame.
Thus, addressing is done on the basis of addresses defined by the user
him/herself. The added header contains 6 bytes in total, terminating
with the ingress and egress addresses, preceded by the hop count and a
flag.
The Ethernet frames are recovered after decapsulation at their
egress. Thus, we see a classic mode of forwarding – either using the
VLAN number, with the Ethernet address serving as a reference, or
decapsulating the Ethernet frame to retrieve the IP packet.
An interesting point is the possibility to transfer the frames from
the same flow using several paths simultaneously: this is known as
multipath, or ECMP (Equal Cost MultiPath), which enables us to
detect the different paths of equal cost and point the frames along
these various paths.
4.7. LISP (Locator/Identifier Separation Protocols)
LISP (Locator/Identifier Separation Protocol) was developed to
facilitate the transport of virtual machines from one datacenter to
another without changing the IP address of the virtual machine. In
order for this to work, we need to separate the two interpretations of
the IP address: the identifier of the user machine and the locator used
for routing. If we wish to preserve the address of the virtual machine,
it is necessary to differentiate these two values. This is what LISP
does, but it is not the only protocol to do so: HIP (Host Identity
Protocol) and SHIM6 (Level 3 Multihoming Shim Protocol for IPv6)
also differentiate the two interpretations, but with mechanisms based
on the destination machines.
With LISP, the routers take care of the association between the
address of the destination machine – the EID (Endpoint ID) – and the
address used for routing – the RLOC (Routing-Locator). When a
communication is begun between an addressee machine and a server
machine, the traffic is intercepted by an “iTR” (ingress Tunnel
Router), which must determine the appropriate RLOC to access the
server machine, whose address is that of the EID. The network egress
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opposed to the convention 6 bytes occupied by the Ethernet frame.
Thus, addressing is done on the basis of addresses defined by the user
him/herself. The added header contains 6 bytes in total, terminating
with the ingress and egress addresses, preceded by the hop count and a
flag.
The Ethernet frames are recovered after decapsulation at their
egress. Thus, we see a classic mode of forwarding – either using the
VLAN number, with the Ethernet address serving as a reference, or
decapsulating the Ethernet frame to retrieve the IP packet.
An interesting point is the possibility to transfer the frames from
the same flow using several paths simultaneously: this is known as
multipath, or ECMP (Equal Cost MultiPath), which enables us to
detect the different paths of equal cost and point the frames along
these various paths.
4.7. LISP (Locator/Identifier Separation Protocols)
LISP (Locator/Identifier Separation Protocol) was developed to
facilitate the transport of virtual machines from one datacenter to
another without changing the IP address of the virtual machine. In
order for this to work, we need to separate the two interpretations of
the IP address: the identifier of the user machine and the locator used
for routing. If we wish to preserve the address of the virtual machine,
it is necessary to differentiate these two values. This is what LISP
does, but it is not the only protocol to do so: HIP (Host Identity
Protocol) and SHIM6 (Level 3 Multihoming Shim Protocol for IPv6)
also differentiate the two interpretations, but with mechanisms based
on the destination machines.
With LISP, the routers take care of the association between the
address of the destination machine – the EID (Endpoint ID) – and the
address used for routing – the RLOC (Routing-Locator). When a
communication is begun between an addressee machine and a server
machine, the traffic is intercepted by an “iTR” (ingress Tunnel
Router), which must determine the appropriate RLOC to access the
server machine, whose address is that of the EID. The network egress
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