Saturday, 25 April 2020
Wednesday, 22 April 2020
EIGRP
Enhanced Interior
Gateway Routing Protocol (EIGRP) is still a part of CCNP/CCIE curriculum so I
am using this post for exam preparation or trouble shooting purposes. Believe it or not you can still see this protocol being in use in
commercial environments but it is not part of the new Cisco CCNA exam.
About EIGRP:
- EIGRP replaced IGRP in
1993, initially Cisco proprietary now partially open standard
described in RFC7868 classless
routing protocol
-
Hybrid routing
protocol/Advanced distant routing protocol
-
uses DUAL algorithm
(Diffusing update algorithm)
-
uses protocol number 88
-
protocol independent, uses
multicast address 224.0.0.10 and FF02::A for IPv6
-
Supports unequal load
balancing (Advantage over link-state protocols)
-
provides fast convergence
(Advantage over link-state protocols)
EIGRP terminology:
-
Successor – next-hop router with the lowest path metric
-
Feasible Successor (FS) – backup
route to the destination
-
Reported Distance (RD) – cost
between next hop and a destination
-
Feasible distance (FD) – cost
to the destination (cost to the next hop + RD)
-
Active route – route for
which Query process is being used to find a loop free alternative route (i.e.
when the link goes down)
-
Passive route – route that
is ready to be used (no longer calculated by DUAL)
EIGRP Tables:
-
Neighbor Table – lists of
all neighbors
-
Topology Table – list of
all prefixes
-
Routing Table – best
routes (Successors)
EIGRP Packet types:
Uses RTP (Reliable Transport Protocol) to exchange information
-
Hello – forms relationship / keep alive
-
Update – updates can be
partial or full routing table (only sent when forming neighbour)
-
Query – i.e. query is send
when there is no Feasible Successor (FS)
-
Replay – response to the
query
-
Ack – acknowledgment to
the update, query or reply messages
EIGRP Metric
calculation
-
by default Bandwidth
and Delay are being used, K1 and K3 both have the value of 1
-
by default K2, K4 and K5
are set to 0
-
latency is measured in microseconds, reference bandwidth 10Gbps
EIGRP Wide metrics
-
was implemented to help
with higher-capacity links(up to 655Tbps), K6 value was added
-
by default K6 is 0 which
makes it backward compatible
-
latency is measured in
picoseconds
EIGRP
troubleshooting (things to
remember)
-
by default hello timer is
5 seconds (60sec on older slower links)
-
hold timer is 3x Hello
timer
-
to form neighbor
relationship EIGRP ASN numbers must match, K values must match, if
authentication is used password and keys must match
-
when router detects the
loss of Successor, Feasible Successor is being used and the Update
is being send and every router that receive it will run DUAL
-
when router detects the
loss of Successor and there is no Feasible Successor, route state
changes from passive to active and DUAL will send a Query
to EIGRP neighbors
Stuck in active (SIA) – this happens when there is no reply within 3 minutes often caused by high CPU and memory usage, packet drop or unidirectional links.
Wednesday, 15 April 2020
Multicast - Part 1
Multicast
transmission is communication a method that allows send traffic from the source
to the group of receivers simultaneously. Multicast communication relays on
Internet Group Management Protocol (IGMP) and Protocol Independent Multicast (PIM).
IP Multicast concept:
-receivers use Internet Group
Management Protocol (IGMP) to join multicast groups – Layer 2
-protocol Independent Multicast
(PIM) is used to route multicast traffic(Layer 3)
-only members of the group
receive data
-once send information to the
group address all members receive it
-non members can send information
to a group
-source address can never be a
Class D multicast group address.
IPv4 address
space reserved for Multicast is 224.0.0.0 – 239.255.255.255 (Class D) which includes:
1. 224.0.0.0
– 224.0.0.255 – Reserved Link-Local Address ie:
- 224.0.0.5 –
used by OSPF all routers
-224.0.0.6 –
used by OSPF DRs
-224.0.0.9 –
used by RIP
-224.0.0.10 –
used by EIGRP
-224.0.0.13 –
All PIM routers
2. 224.0.1.0
– 238.255.255.255 – Globally Scoped Addresses
a) 224.0.1.0 - 224.0.1.255 - Internetwork
Control Block i.e.:
-224.0.1.1 –
NTP Network Rime Protocol
-224.0.1.32 –
Mtrace routers
-224.0.1.39 –
cisco-rp-announce
-224.0.1.40 -
cisco-rp-discovery
b) 232.0.0.0
– 232.255.255.255 – Source Specific Multicast (SSM) addresses, default range
used by SSM which is a PIM extension (RFC 4607)
c)233.0.0.0 –
233.255.255.255 – GLOP Block (The assignment is made, for a domain with a 16bit
Autonomous System Number (ASN))
d)
239.0.0.0-239.255.255.255-Administratively
Scoped IP addresses
More details about IPv4 addresses (IANA):
https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml#multicast-addresses-2
Internet Group Management Protocol (IGMP) is the layer 2 protocol
used by receivers to join multicast groups (i.e. between the receiver and its gateway).
We have tree versions on IGMP,
here is the brief:
-
in IGMPv1 – JOIN message is send to the router,
there is a 60s timer on the router that will request an update from the
receiver if it still needs to belong to the group
-
in IGMPv2 – Receiver sends JOIN group message as
well as the LEAVE group message
-
in IGMPv3 – Receiver sends JOIN group message,
LEAVE group message and define SOURCE IP for multicast traffic (if there is
more than one source), two different
modes are available: include mode and exclude mode.
IGMP snooping is used by i.e. switch to learn about multicast
traffic so it can use the information to be forwarded to receivers, benefits:
-Optimized bandwidth utilization
-Security – prevents denial of
service attacks from unknown sources
IGMP filtering can be used to control:
-
specific multicast groups membership
-
number
of multicast groups per port/interface
-
version
of IGMP allowed
What is Protocol Independent Multicast (PIM)?
-
multicast routing protocol necessary to route
multicast traffic used by routers to locate and request multicast streams utilize Distribution Trees that define the path
that multicast traffic follows through the network. There are two types of
distribution trees: source trees (Shortest Path Trees - SPT) and shared trees
(RPT)
PIM control messages:
-
use IP protocol 103
-
unicast or multicast
-
TTL value of 1
-
All PIM router address 224.0.0.13
-
by default “Hello” messages are being send every
30 seconds
Source three – multicast distribution tree often referred as SPT,
source is the root of the tree and the branches are all the way through the
network to receivers, known by the notation (S, G) where “S” is the source and
“G” is the multicast group
Shared trees – multicast distribution tree where the root is the
designated router as the rendezvous point (RP) not the source (S) of the
multicast traffic. Shared trees are also known as RP trees (RPTs). Traffic is
being forwarded to the group address regardless of the source, notation (*,G).
Advantage is that RPT require fewer multicast entries (*,G) and (S,G). Downside
is that receivers receive traffic from all multicast sources which will cause
lots of unwanted traffic, waste of bandwidth and also it opens potential
security risk (unwanted packets send to receivers).
PIM operating modes:
-
PIM dense Mode
-
PIM Sparse Mode
-
PIM Sparse Dense Mode
-
PIM Bidirectional Mode
-
PIM Source Specific Multicast Mode
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