CCNP-SWITCHING 300-115
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Double CCIEs #27042(R/S&SP)
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Part IV: Multilayer
Switching
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Multilayer Switching
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Inter-VLAN Routing
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Types of Interfaces
Layer 2 Port Configuration
Switch(config)# interface type
member/module/number
Switch(config-if)# switchport
Layer 3 Port Configuration
Switch(config)# interface type
member/module/number
Switch(config-if)# no switchport
Switch(config-if)# ip address ip-address mask
[secondary]
SVI Port Configuration
Switch(config)# interface vlan vlan-id
Switch(config-if)# ip address ip-address mask
[secondary]
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Multilayer Switching with CEF
Traditional MLS Overview
dual effort between a route processor (RP) and a switching engine (SE).
“route once and switch many.”
SE must know the identity of each RP
it can learn a “shortcut path”
also is known as NetFlow switching or route cache switching.
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CEF Overview Cisco Express
Forwarding.
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A CEF-based multilayer
switch consists of two
basic functional blocks
1-Forwarding
Information Base
Reformat the routing
table into an ordered list
with the most specific
route first
FIB also contains the
next-hop address for
each entry
FIB also contains host
route (subnet mask
255.255.255.255) most
efficient routing lookup
to directly connected or
adjacent hosts.
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1-Forwarding Information Base
FIB
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Switch# show ip cef vlan 101
Prefix Next Hop Interface
10.1.1.0/24 attached Vlan101
10.1.1.2/32 10.1.1.2 Vlan101
10.1.1.3/32 10.1.1.3 Vlan101
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Switch# show ip cef 10.1.0.0 255.255.0.0 longer-prefixes
Prefix Next Hop Interface
10.1.1.0/24 attached Vlan101
10.1.1.2/32 10.1.1.2 Vlan101
10.1.1.3/32 10.1.1.3 Vlan101
10.1.2.0/24 attached Vlan102
10.1.3.0/26 192.168.1.2 Vlan99
192.168.1.3 Vlan99
10.1.3.64/26 192.168.1.2 Vlan99
192.168.1.3 Vlan99
10.1.3.128/26 192.168.1.4 Vlan99
192.168.1.3 Vlan99
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FIB cont.
Switch# show ip cef 10.1.3.0 255.255.255.192 detail
10.1.3.0/26, version 270, epoch 0, per-destination sharing
0 packets, 0 bytes
via 192.168.1.2, Vlan99, 0 dependencies
traffic share 1
next hop 192.168.1.2, Vlan99
valid adjacency
via 192.168.1.3, Vlan99, 0 dependencies
traffic share 1
next hop 192.168.1.3, Vlan99
valid adjacency
0 packets, 0 bytes switched through the prefix
tmstats: external 0 packets, 0 bytes
internal 0 packets, 0 bytes
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The version number describes the number of times the CEF entry has been updated since the
table was generated.
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The epoch number denotes the number of times the CEF table has been flushed and
regenerated as a whole
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This follows the hardware switching process, in which no “expensive” or time-consuming
operations are needed.
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FIB cont.
• “CEF punt” sent to the Layer 3 engine for further processing,
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An entry cannot be located in the FIB.
The FIB table is full.
The IP Time-To-Live (TTL) has expired.
The maximum transmission unit (MTU) is exceeded, and the packet
must be fragmented.
An Internet Control Message Protocol (ICMP) redirect is involved.
The encapsulation type is not supported.
Packets are tunneled, requiring a compression or encryption
operation.
An access list with the log option is triggered.
A Network Address Translation (NAT) operation must be performed
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FIB cont.
• CEF also can be optimized through the use of specialized
forwarding hardware
• Accelerated CEF (aCEF): distributed across multiple Layer 3
forwarding engines
• These engines do not have the capability to store and use
the entire FIB,
• This functions as an FIB “cache,” containing entries that are
likely to be used again
• If FIB entries are not found in the cache, requests are sent
to the Layer 3 engine for more FIB information.
• Distributed CEF (dCEF):completely among multiple Layer 3
• the Catalyst 6500 has line cards that support dCEF,
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Adjacency Table
• FIB has corresponding Layer 2 information for
every next-hop entry This portion of the
• FIB is called the adjacency table, consisting of
the MAC addresses of nodes that can be
reached in a single Layer 2 hop.
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Adjacency Table
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Switch# show ip arp 10.1.1.2
Switch# show ip cef 10.1.1.2
255.255.255.255 detail
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10.1.1.2/32, version 688, epoch 0,
attached, connected
0 packets, 0 bytes
via Vlan101, 0 dependencies
valid glean adjacency
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CEF glean state waiting for the
ARP resolution, This is called
ARP throttling or throttling
adjacency.
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If an ARP reply is not received
in 2 seconds, the throttling is
released so that another ARP
request can be triggered
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Following adjacency types listed
• Null adjacency: Used to switch packets destined
for the null interface.
• Drop adjacency: Used to switch packets that
cannot be forwarded normally
• Discard adjacency: Used when packets must be
discarded because of an access list or other
• policy action
• Punt adjacency: Used when packets must be sent
to the Layer 3 engine for further processing
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Punt adjacency
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No_adj: An incomplete adjacency
No_encap: An incomplete ARP resolution
Unsupp’ted: Unsupported packet features
Redirect: ICMP redirect
Receive: Layer 3 engine interfaces; includes packets
destined for IP addresses that are assigned to
interfaces on the Layer 3 engine, IP network addresses,
and IP broadcast addresses
Options: IP options present
Access: Access list evaluation failure
Frag: Fragmentation failure
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Packet Rewrite
• Layer 2 destination address: Changed to the
next-hop device’s MAC address
• Layer 2 source address: Changed to the
outbound Layer 3 switch interface’s MAC address
• Layer 3 IP TTL: Decremented by one because one
router hop has just occurred
• Layer 3 IP checksum: Recalculated to include
changes to the IP header
• Layer 2 frame checksum: Recalculated to include
changes to the Layer 2 and Layer 3 headers
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© 2015 Mohamed Samir YouTube channel
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Any questions ?
Mohamed Samir
© 2015 Mohamed Samir YouTube channel
All rights reserved.
www.mohamedsamir.com
Thank you
for your
time ! 
‫شكرا‬
‫جزاكم هللا خير‬
Mohamed Samir
© 2015 Mohamed Samir YouTube channel
All rights reserved.
www.mohamedsamir.com