09-21-2015 07:34 AM - edited 03-05-2019 02:21 AM
I have a 2951 routers with 3 T1's connected to controller cards/serial interfaces. How does the router determine which serial interface to use?
09-21-2015 08:00 AM
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Posting
By examination of your route table, i.e. which interface, or interfaces, is best next hop toward packet's destination.
09-21-2015 08:13 AM
More information
I am thinking CEF will be involved. I but I haven't seen how CEF is balancing the load.
interface Multilink1
bandwidth 4608
ip address 1.1.1.21 255.255.255.252
ip flow ingress
ip flow egress
no peer neighbor-route
ppp chap hostname *
ppp multilink
ppp multilink interleave
ppp multilink group 1
no cdp enable
service-policy output qos_pm
hold-queue 256 in
hold-queue 4096 out
interface Serial0/0/0:0
no ip address
encapsulation ppp
ppp chap hostname *
ppp multilink
ppp multilink group 1
hold-queue 256 in
hold-queue 4096 out
interface Serial0/0/1:1
no ip address
encapsulation ppp
ppp chap hostname *
ppp multilink
ppp multilink group 1
hold-queue 256 in
hold-queue 4096 out
interface Serial0/1/0:2
no ip address
encapsulation ppp
ppp chap hostname *
ppp multilink
ppp multilink group 1
hold-queue 256 in
hold-queue 4096 out
Multilink1 is up (if_number 43)
Corresponding hwidb fast_if_number 43
Corresponding hwidb firstsw->if_number 43
Internet address is 1.1.1.21/30
ICMP redirects are never sent
Per packet load-sharing is disabled
IP unicast RPF check is disabled
Input features: Ingress-NetFlow
Output features: CCE Post NAT Classification, QoS Marking, Post-Ingress-NetFlow, Egress-Netflow
IP policy routing is disabled
BGP based policy accounting on input is disabled
BGP based policy accounting on output is disabled
Interface is marked as point to point interface
Hardware idb is Multilink1
Fast switching type 7, interface type 105
IP CEF switching enabled
IP CEF switching turbo vector
IP Null turbo vector
IP prefix lookup IPv4 mtrie 8-8-8-8 optimized
Input fast flags 0x0, Output fast flags 0x10004000
ifindex 41(41)
Slot Slot unit 1 VC -1
IP MTU 1500
IPv4 CEF is enabled and running
VRF Default
491 prefixes (490/1 fwd/non-fwd)
Table id 0x0
Database epoch: 0 (491 entries at this epoch)
0.0.0.0/0, epoch 0, flags cover dependents, rib only nolabel, rib defined all labels, default route, RIB[B], refcount 7, per-destination sharing
sources: RIB, DRH
feature space:
IPRM: 0x00018000
NetFlow: Origin AS 0, Peer AS 0, Mask Bits 0
subblocks:
Covered dependent prefixes: 1
notify cover updated: 1
ifnums:
Multilink1(43)
path 1BCB1E0C, path list 1BBB5A38, share 1/1, type recursive, for IPv4
recursive via 1.1.1.22[IPv4:Default], fib 1BBC2038, 1 terminal fib, v4:Default:1.1.1.22/32
path 1BCB2FFC, path list 1BBB5CB8, share 1/1, type recursive, for IPv4, flags doesnt-source-via, cef-internal
recursive via 1.1.1.20/30<nh:1.1.1.22>[IPv4:Default], fib 1BBC70A8, 1 terminal fib, v4:Default:1.1.1.20/30
path 1BCB0CFC, path list 1BBB4688, share 1/1, type connected prefix, for IPv4
connected to Multilink1, adjacency IP adj out of Multilink1 1BB465A0
output chain:
loadinfo 0233303C, per-session, 1 choice, flags 0183, 260 locks
flags: Per-session, for-rx-IPv4, 2buckets, indirection
1 hash bucket
< 0 > IP adj out of Multilink1 1BB465A0
Subblocks:
None
09-21-2015 08:39 AM
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The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
Ah, your three T1 appear to be configured as MLPPP. From a routing perspective, there's only one link.
I believe MLPPP load balances by sending packets to the next available physical interface.
09-21-2015 08:54 AM
Any show commands you can suggest?
show ppp multilink - the weight of each serial interface (equal).
Ultimately, I am trying to figure why my 4.6 Mbps (3 T1's) are not fully utilized during afterhours system backups. Some offices use the maximum bandwidth, other do not.
Multilink1
Bundle name: 5B3EA11C45316A0B294597F30000002800000065
Remote Endpoint Discriminator: [4] 5B3EA11C45316A0B294597F30000002800000065
Local Endpoint Discriminator: [1] 204.64.155.21cpa
Bundle up for 8w0d, total bandwidth 4608, load 17/255
Receive buffer limit 36000 bytes, frag timeout 1000 ms
Interleaving enabled
0/0 fragments/bytes in reassembly list
1190 lost fragments, 87647793 reordered
0/0 discarded fragments/bytes, 0 lost received
0x4E59EB received sequence, 0x4BA5B0 sent sequence
Member links: 3 active, 0 inactive (max 255, min not set)
Se0/0/0:0, since 8w0d, 5760 weight, 1496 frag size
Se0/0/1:1, since 3w3d, 5760 weight, 1496 frag size
Se0/1/0:2, since 01:45:23, 5760 weight, 1496 frag size
No inactive multilink interfaces
09-21-2015 09:46 AM
Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
If TCP, that might be caused by some clients' stacks not supporting your BDP.
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