A load balancer is a device that acts as a reverse proxy and distributes network or application traffic across a number of servers. Load balancers are used to increase capacity (concurrent users) and reliability of applications. They improve the overall performance of applications by decreasing the burden on servers associated with managing and maintaining application and network sessions, as well as by performing application-specific tasks.
Load balancers are generally grouped into two categories: Layer 4 and Layer 7. Layer 4 load balancers act upon data found in network and transport layer protocols (IP, TCP, FTP, UDP). Layer 7 load balancers distribute requests based upon data found in application layer protocols such as HTTP.
Requests are received by both types of load balancers and they are distributed to a particular server based on a configured algorithm. Some industry standard algorithms are:
Round robin
Weighted round robin
Least connections
Least response time
Layer 7 load balancers can further distribute requests based on application specific data such as HTTP headers, cookies, or data within the application message itself, such as the value of a specific parameter.
Load balancers ensure reliability and availability by monitoring the &health& of applications and only sending requests to servers and applications that can respond in a timely manner.
hint: access search faster by typing ctrl+shift+fposed a question on Twitter today:
Does anyone have any opinion or pointers for HP Procurve 2900s? Had issues setting up LACP trunks w/c2960s, opted for single connections..
I thought I had written up how to configure LACP between HP and Cisco switches before, but after checking I realized that I didn’t. What I had mentioned was a “gotcha” regarding
(a.k.a. “the wrong way”).
After a frantic search for an HP console cable (someone was “nice enough” to “organize” my office a bit while I was recently out of state), I decided to lab it up and write about it (surely someone will need to do this at some point).
I’m not going to bother with drawing up a diagram in Visio — hopefully you engineers can imagine three cables connecting the two switches. I’m using interfaces 1, 2, and 3 on the HP side and fa0/1, fa0/2, and fa0/3 on the Cisco side.
Let’s start with the Cisco side of things, since that’s probably what most people are familiar with.
CISCO(config)# interface range fa0/1 - 3
CISCO(config-if-range)# spanning-tree portfast trunk
%Warning: portfast should only be enabled on ports connected to a single
host. Connecting hubs, concentrators, switches, bridges, etc... to this
when portfast is enabled, can cause temporary bridging loops.
Use with CAUTION
CISCO(config-if-range)# channel-protocol lacp
CISCO(config-if-range)# channel-group 1 mode active
Creating a port-channel interface Port-channel 1
CISCO(config-if-range)# interface port-channel 1
CISCO(config-if)# switchport mode trunk
CISCO(config-if)#
Let’s go ahead and create a few VLANs to trunk across our link:
CISCO(config-if-range)# vlan 10
CISCO(config-vlan)# vlan 20
CISCO(config-vlan)# vlan 30
CISCO(config-vlan)#
I’ll configure an IP address on the VLAN 1 interface so that we can generate some traffic to send across and verify our link is operational.
CISCO(config-vlan)# interface vlan 1
CISCO(config-if)# ip address 10.0.0.1 255.255.255.0
CISCO(config-if)# no shutdown
CISCO(config-if)#
00:13:03: %LINK-3-UPDOWN: Interface Vlan1, changed state to up
00:13:04: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up
CISCO(config-if)#
Now we can move over to the HP side and create an LACP “trunk”. Note that HP uses different terminology and a “trunk” refers to an aggregated link.
HP(config)# trunk 1-3 trk1 lacp
HP(config)#
Create the same VLANs we did on the Cisco side and tell the switch to pass those VLANs across our aggregated link with 802.1Q tags inserted into their frames (e.g. “tagged”):
HP(config)# vlan 10
HP(vlan-10)# tagged trk1
HP(vlan-10)# vlan 20
HP(vlan-20)# tagged trk1
HP(vlan-20)# vlan 30
HP(vlan-30)# tagged trk1
HP(vlan-30)#
While we’re here, I’ll go ahead and configure the IP address for VLAN 1 as well:
HP(config)# vlan 1
HP(vlan-1)# ip address 10.0.0.2 255.255.255.0
HP(vlan-1)#
On the Cisco side, I’ll run a debug so that we can see exactly what happens as I plug in the cables (note that all the interfaces are already enabled):
CISCO(config-if)# debug etherchannel event
PAgP/LACP Shim Events debugging is on
CISCO(config-if)#
*Jeremy gets up, walks over, and plugs in the cables.*
00:48:18: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
00:48:19: FEC: pagp_switch_port_up: Fa0/1
00:48:19: FEC: pagp_switch_invoke_port_up: Fa0/1
00:48:19: FEC: lacp_switch_add_port_to_associated_list: Fa0/1 added to list
00:48:21: FEC: lacp_switch_add_port_to_agport_internal: Fa0/1 added to
aggregator Po1 list
00:48:22: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1,
changed state to up
00:48:23: %LINK-3-UPDOWN: Interface Port-channel1, changed state to up
00:48:24: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1,
changed state to up
00:48:33: %LINK-3-UPDOWN: Interface FastEthernet0/2, changed state to up
00:48:34: FEC: pagp_switch_port_up: Fa0/2
00:48:34: FEC: pagp_switch_invoke_port_up: Fa0/2
00:48:34: FEC: lacp_switch_get_first_agg_id_from_admin_oper_keys: found
aggregator Po1 for admin_key [0x1] and oper_key [0x1]
00:48:34: FEC: lacp_switch_get_first_associated_port_from_agg_id: found
port Fa0/1 associated to Po1
00:48:34: FEC: lacp_switch_add_port_to_associated_list: Fa0/2 added to
list for Po1
00:48:36: FEC: lacp_switch_add_port_to_agport_internal: Fa0/2 added to
aggregator Po1 list
00:48:37: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2,
changed state to up
00:48:48: %LINK-3-UPDOWN: Interface FastEthernet0/3, changed state to up
00:48:49: FEC: pagp_switch_port_up: Fa0/3
00:48:49: FEC: pagp_switch_invoke_port_up: Fa0/3
00:48:49: FEC: lacp_switch_get_first_agg_id_from_admin_oper_keys: found
aggregator Po1 for admin_key [0x1] and oper_key [0x1]
00:48:49: FEC: lacp_switch_get_first_associated_port_from_agg_id: found
port Fa0/1 associated to Po1
00:48:49: FEC: lacp_switch_add_port_to_associated_list: Fa0/3 added to
list for Po1
00:48:51: FEC: lacp_switch_add_port_to_agport_internal: Fa0/3 added to
aggregator Po1 list
00:48:52: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3,
changed state to up
Let’s send some pings across the link:
CISCO(config-if)# do ping
Protocol [ip]:
Target IP address: 10.0.0.2
Repeat count [5]: 10000
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 1-byte ICMP Echos to 10.0.0.2, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
... (output removed) ...
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Success rate is 100 percent (), round-trip min/avg/max = 4/5/36 ms
CISCO(config-if)#
Last, we can use show etherchannel summary to verify the configuration of our aggregated link:
CISCO(config-if)# do show etherchannel summary
P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3
S - Layer2
u - unsuitable for bundling
U - in use
f - failed to allocate aggregator
d - default port
Number of channel-groups in use: 1
Number of aggregators:
Port-channel
------+-------------+-----------+---------------------------------------
I hope this was helpful (and correct!) as I did it in quite a hurry and got pulled away for a few minutes in the middle of doing it and had to try to remember where I left off!
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