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Could you explain tree-spanning?
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Bridges filter input and output traffic so that only data frames
distended for another network segment are actually routed into that
segment and only data frames destined for the outside are allowed
out of the network segment. The performance of a bridge is governed
by two main factors:
The filtering rate. A bridge reads the MAC address of the
Ethernet/Token ring/FDDI node and then decides if it should forward
the frames into the network. Filter rates for bridges range from
around 5000 to 70000pps (packets per second).
The forward rate. Once the bridge has decided to route the
frame into the internetwork, the bridge must forward the frame onto
the destination network. Forwarding rates range from 500 to 140,000pps
and a typical forwarding rate is 90,000pps.
An example Ethernet bridge has the following specifications:
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Bit rate:
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10Mbps
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Filtering rate:
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17500pps
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Forwarding rate:
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11000pps
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Connectors:
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Two DB15 AUI (female), one DB9 male console port, two BNC
(for 10BASE2) or two RJ-45 (for 10BASE-T).
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Algorithm:
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Spanning tree protocol. This automatically learns the addresses
of all devices on both interconnected networks and builds
a separate table for each network.
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Spanning tree architecture (STA) bridges
The IEEE 802.1 standard has defined the spanning tree algorithm,
and is normally implemented as software on STA-compliant bridges.
On power-up they automatically learn the addresses of all the nodes
on both interconnected networks and build up a separate table for
each network.
They can also support two connections between two LANs so that
when the primary path becomes disabled, the spanning tree algorithm
re-enables the previously disabled redundant link, as illustrated
in Figure 1.
Figure 1: Spanning-tree bridges
Source route bridging
With source route bridging, a source device, not the bridge, is
used to send special explorer packets. These are then used to determine
the best path to the destination. Explorer packets are sent out
from the source routing bridges until they reach their destination
workstation. Each source routing bridge along the route enters its
address in the routing information field (RIF) of the explorer packet.
The destination node then sends back the completed RIF field to
the source node. When the source device has determined the best
path to the destination, it sends the data message along with the
path instructions to the local bridge, which then forwards the data
message according to the received path instructions.
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Could you explain how routers deal with ARP request?
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Friday, January 12, 2001 at 10:39:02
Routers react to ARP requests in the same way that
any other host does. They will only respond to an ARP request if
one of their ports has the IP address which is contained in the
ARP request. They listen to all the ARP replies, though, and will
update their ARP table whenever they hear an ARP reply. If they
do not know the MAC address of a host on the network then they will
send out an ARP request to find it. If it cannot find the host,
it will discard the incoming message (as the host either doesn't
exist or has went off-line).
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What is the difference between a switch and hub?
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Monday, January 15, 2001 at 16:31:05
A hub operates a Level 1 of the OSI model and basically
just provides a basic network connection. Thus it still has collision
between the ports of the hub. A switch operates at Layer 2 of the
OSI model, and allows simulataneous communications between pairs
of ports (and thus does not have any collisions). Thus a 10Mbps
switch can support multiples of this bandwidth if two or more nodes
are communicating at a time. The layers are really:
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Layer 1
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Hub, which basically just creates a network connection,
and propagates collisions)
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Layer 2
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Switch, which operates on the MAC address, and switches
data between connected ports. Switches can either be cut-through,
where the data frame is forwarded immediately as the destination
MAC address is read, or store-and-forward where the data frame
is stored in memory before it is forwarded.
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Layer 3
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Router, which uses the network address to route data.
These will operate at a slower rate than switches as they
must look inside the data packet before it can be forwarded
to another port.
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what is the differnce between the switch and the bridge?
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Wednesday, January 24, 2001 at 06:52:09
Bridges and switches have similarities:
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They isolate collision domains. Both a bridge and
a switch contain collisions within a network segment.
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They transmit broadcasts from one network segment
to another (leading to a broadcast storm on the network).
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They learn where nodes are located based on MAC
addresses.
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The big difference is that switches allow simultaneous
communications between any two nodes, at the same time. Also switches
are used to create LANs (in the same way that a hub does), whereas
bridges are used to segment networks. Thus a switch is optimised
to communicate with individual nodes, whereas a bridge interfaces
to network segments. Switches can also be used to create vLANs where
collisions are completely elliminated, and broadcast domains can
be programmed by software. This enhances security, uses the bandwidth
more efficiently, and so on. Bridges also are setup so that they
can sense when there is multiple route to a destination, and can
easily switch between the two, when one become inoperative (this
uses the Spanning-tree protocol).
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If we had a 9 ports Hub with a built in fibre optic transceiver.
9 nodes are connected to that hub, and on the other
end similar hub connected to that hub by the fibre optic link.
The bandwidth of each hub is 10 mbs.
now if nodes A,B,C,.....(up to nine nodes connected to the
1st HUb) and nodes A transferring files to node B, the rest
of nodes are doing nothing.
Am I right in that A & B will be communicating in
Simi duplex mode , using 10 MBS at a time , i.e. Nodes A
send the inform at 10MBS on its TX pair, the hub receives
it on Its RXing Pairs and will put it out to every other ports
on its TX pair except the one that generate that traffic.
If other start communicating , the procedure would be
same as only one node can send traffic at a time.
My confusion relate to the term sharing the band width,
if a lot traffic is going back and forward, each node will
still be using 10MBS but will have a less access , am I right
in believing that when they talk a bout sharing the B.W, that
is what they mean, or they mean 10mbs divide between 10 nodes
and each gets 1mbs?
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Wednesday, May 30, 2001 at 08:00
A hub is basically just the same as have a common
cable which connects all the nodes to the common bus. Thus if two
nodes transmit at the same time they will cause a collision, and
no nodes can transmit. Each of the nodes which caused the collision
will wait for a ramdom period before getting access to the network.
The key is that the transmit at a rate of 10Mbps, but THEY ONLY
TRANSMIT ONE DATA FRAME (which is a maximum of 1500 bytes). Thus
after they transmit this frame they must contend to get access to
the network. Thus if the network is busy they might not get access
for some time. As the traffic increases on the network, there will
be more collision, thus there will be more wasted time. Thus causes
the maximum throughput to reduce to around 5Mbps.
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The other question is related to the built in Transceiver,
when node A sends the info to the Hub, does the transceiver
convert these info and send it at a dedicated 10mbs at the
same time the hub rebroadcast the info at 10MBS on all the
other ports or does the transceiver share the BW with other
ports.
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Wednesday, May 30, 2001 at 08:00
In a hub all the transmit lines are connected together, thus if
the node detects a collision on its RX line, it stops transmitting
and sends a jamming signal to the rest of the network. It is thus
important for the node to 'listen' to the network as it is transmitting.
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When running a show interface on an Ethernet port I get
values for runts and gaints. What are these?
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Wednesday 24 Jan 2001. Semester 2 course.
They are weird tems, but a runt
is an Ethernet frame of less than 64 bytes, and a gaint
is an Ethernet frame with more the 1500 bytes (which is greater
than the MTU of 1500,
in the case below). Some of the other terms are:
Rely
which defines reliability.
BW which defines
bandwidth.
Dly which defines
delay.
Load which defines
the loading.
LAB-A# show
interfaces
Ethernet0 is up, line protocol is up
Hardware is Lance, address is 0010.7b81.1d72 (bia 0010.7b81.1d72)
Internet address is 192.5.5.1/24
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load
1/255
Encapsulation ARPA, loopback not set, keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:43, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
62 packets input, 6425 bytes, 0 no buffer
Received 50 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 input packets with dribble condition detected
261 packets output, 31216 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 lost carrier, 0 no carrier
Ethernet1 is up, line protocol is up
Hardware is Lance, address is 0010.7b81.1d73 (bia 0010.7b81.1d73)
Internet address is 205.7.5.1/24 ... and so on.
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