CS475 – Networks
Lecture 14
Chapter 4 – Advanced Internetworking
Assignments
• Reading for Lecture 15: Sections 5.1- 5.2
• Homework 5, Wireshark Project 3 posted, due next Thursday; Programming Project 3 posted, due following Tuesday
4.2 Multicast
IP supports multicast to support one-to-many (radio, news,
IP multicast was originally a many-to-many (any source MC or
updates) and many-to-many (teleconf, gaming) communication. ASM) model. A one-to-many MC model (source-specific MC or
IP multicast (MC) uses MC groups, where each group has its
SSM) was developed in which a receiver specifies a MC group
own IP MC address.
and a specific host.
A sending host sends a single copy of a packet to the MC
A host joins and leaves an MC group by using (IPv4) Internet
address. The network routers _____________ the packet
Group Management Protocol (______________) or (IPv6) MC
whenever it needs to be forwarded over more than one link.
Listener Discovery (MLD) to communicate to the local router.
4.2.1 Multicast Addresses
4.2.2 Multicast Routing
IPv4 uses addresses 224.0.0.0 through 239.255.255.255 (Class
While a unicast propagates along a path, a multicast propagates
D) for multicast. This address range uses a 4-bit prefix (1110)
along a __________________.
leaving _______________ to specify an MC group.
Multicast routing is the process by which the multicast
Ethernet supports multicast (in addition to unicast and broadcast) distribution tree is determined.
but uses only 23 bits for an MC address. 32 (25) IP MC
addresses map into each Ethernet MC address. After receiving
an MC packet a host must examine the entire IP address to either
accept or reject the MC packet.
4.2.2 Multicast Routing: DVMRP
The Distance Vector Multicast Routing Protocol (DVMRP) is an
extension of distance vector routing to support multicast.
DVMRP is a _______________________________ protocol. In
a flood protocol each router would copy and forward a multicast
packet along all links except the one on which the packet arrived
if and only if the packet arrived over the link that is on the
shortest path to the source.
10/13/2011
1 of 5
Duplicate packets can still be sent to LANs connected to more
We want to prune networks that contain no members of the MC
than one router. DVMRP solves this by requiring one router on group. This can be accomplished by having each member of the
a LAN to be designated as the ________________. Only the
group periodically announce that it is a group member. Parent
parent forwards packets to the LAN.
routers can prune networks that contain no members.
4.2.2 Multicast Routing: PIM-SM
DVMRP does not scale well and Protocol Independent MC
(PIM) was developed in response.
There are dense and _________________ modes (PIM-DM and
PIM-SM). PIM-SM is the dominant MC routing protocol and is
the only one discussed here.
Here R4 sends a join message to the RP. R2 will ____________
In PIM-SM, routers join the MC tree by sending a Join message
to a special router known as the rendezvous point (RP).
MC traffic only along the path from RP to R4. R5's Join will
not propagate farther than R2. R2 will add the path to R5 to the
MC tree.
For MC group G, each router looks at the Join and creates a
forwarding table entry for the shared tree, called a (*, G) entry.
To send a message to the group a host sends a packet addressed
to the MC group to a local _________________________ router
(DR) which encapsulates the message in a Register message
which is tunneled to the RP. The RP removes the packet and
sends it out to the shared tree.
R1 is the DR for the host. The message is _____________ from
R1 to RP at which point it is multicast along the distribution tree.
A host sending a lot of data to the MC group can trigger
construction of a source-specific tree rooted at the DR.
A high data rate from a single source can trigger construction of
a more optimal source specific tree that ______________ the
shared tree. The DR in this case effectively replaces the RP.
A source specific tree that uses the shared tree is shown in (c). A
This tree can be significantly shorter than the original shared
shorter source ________________ tree that replaces the shared
tree.
tree is shown in (d).
10/13/2011
2 of 5
4.2.2 Multicast Routing: MSDP
PIM-SM is typically used only within a domain. The Multicast
Source Discovery Protocol (MSDP) was developed to extend
MC across domains that use PIM-SIM.
Each domain has an RP with peer RPs in other domains. An RP
sends Source Active messages periodically to its peers on behalf
of the sources. A peer can join the MC group by sending a Join
message to DR for the source.
Construction of a source specific MC tree across domains using
______________________
4.2.2 Multicast Routing: PIM-SSM
4.2.2 Multicast Routing: BIDIR-PIM
PIM was originally designed as a many-to-many protocol. PIM Bidirectional PIM (BIDIR-PIM) is an enhancement to PIM that
source-specific multicast (PIM-SSM) was developed to support
is better suited for many-to-many multicasting within a domain
the demand for a ______________________ protocol.
when the senders and receivers may be the same (multiparty
PIM-SSM required changes only to IGMP rather than PIM. In
video-conference).
PIM-SSM a source specific tree is constructed first, bypassing
the construction of a shared tree.
4.3 Multiprotocol Label Switching (MPLS)
MPLS tries to combine some of the properties of virtual circuits
with those of a ___________________ network.
MPLS-enabled routers forward packets by examining short,
fixed-length labels.
MPLS is primarily used for (1) destination-based forwarding, (2)
explicit routing, and (3) virtual private networks and tunnels.
4.3.1 MPLS: Destination Based Forwarding
Router R2 has assigned and advertised labels for certain network
prefixes. Arriving packets have labels attached by R1 (the label
edge router or ___________________).
10/13/2011
3 of 5
The IP longest match lookup algorithm has been replaced by
exact match lookup.
MPLS allows internal ATM switches to be used as IP routers.
(This can be a cost effective way to carry IP traffic on an existing
ATM network.) The switches are now called Label Switched
Conversion of an overlay network that uses ATM switches to a
peer network (no hardware changes are involved).
Routers (________________).
Each MPLS label is associated with a forwarding equivalence
class (FEC). In this example, the FECs are network prefixes.
4.3.2 MPLS: Explicit Routing
R1 now has one next hop instead of five, resulting in simpler
______________________ tables.
4.3.3 MPLS: Virtual Private Networks and Tunnels
MPLS enabled routers also allow a network to use explicit
MPLS enabled routers allow tunnels through a network that can
routing (similar to source routing). R1 can use the Resource
Reservation Protocol (______________) to specify the R4-R5
path to R7. R2 can specify the R6 path. R1 and R2 attach
carry ______________________ data (ATM cells, Ethernet or
Frame Relay frames).
IP tunnels can be used similarly, but MPLS tunnels use a much
different labels to their packets.
shorter packet header.
The FEC is now based on the source router instead of the
destination
Tunneling of ATM cells through an MPLS tunnel. A _________
label (DL) identifies the virtual circuit. The tunnel label (TL) is
a standard MPLS label.
An ISP can use a network of MPLS enabled routers to create
__________________ networks for customers. A common
infrastructure is used, but each customer appears to have their
own private network.
10/13/2011
4 of 5
4.4 Routing among Mobile Hosts
Other applications would break if we assigned a new IP address
________ has been a key enabling technology that has made
to a host when it moves to a new network. For example, Voice
wireless hotspots feasible. It provides an IP address and the
over IP telephone calls, when a device moves between hotspots
identities of a default router and DNS server for new devices on or switches from wireless to 3G
a network. This is adequate for a large class of applications.
An example is shown at the right. The correspondent's packets
need to be re-routed to the receiver's new network. The
_________ group developed a procedure that allows a host to
keep its original IP address as it moves between networks.
Applications then continue to work seamlessly.
4.4.2 Routing to Mobile Hosts
Mobile IP requires special routers known as the _____________
and foreign agent respectively. The home agent intercepts
packets intended for the mobile host and tunnels the packets to
the foreign agent. The foreign agent delivers the packets to the
host.
4.4.2 Routing to Mobile Hosts - Optimization
Optimizing routes between correspondent node and mobile
4.4.2 Routing to Mobile Hosts - Mobility in Ipv6
Mobility is designed into IPv6. Any IPv6-capable host can
nodes is referred to as the triangle routing problem, since Mobile acquire an address whenever it is attached to a foreign network
IP path takes two side of a triangle rather than the direct path.
and can act as a foreign agent.
The solution is to tell the correspondent node the
Packets to the care-of address can contain an extension header
____________________ of the mobile node. Then the
with the home address. This allows the mobile node to present
correspondent node can create its own tunnel directly to the
the illusion that its IP address is fixed to the higher protocol
mobile node. In the best case, if they are on the same network,
layers.
the packets are addressed directly.
In-class Exercises: Start Homework 5
10/13/2011
5 of 5