Port bounce

what is port bounce ????
Mohammed ShafayNetwork EngineerAsked:
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David SankovskySenior SysAdminCommented:
A Port Bounce is when a switch / Router momentarily stops providing current to a certain port and the returns it, essentially disabling the port for a second and then re-enabling it.

As far as I know, most managed switches allow this, but not Juniper.
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kenfcampCommented:
In addition to what David Sankovsky provided,

Port bouncing is used commonly in networks containing VLANs as a way to force clients to reinitiate DHCP requests when changes have been made
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JustInCaseCommented:
Juniper can bounce port.
It is a little bit longer process if you are trying to use JunOS for shut no shut (but there is a workaround to be faster).

Port bounce in Cisco would be perform shut no shut
interface gi1/0/1
 shut
 no shut

Juniper operation would be (commit takes time)
set interface ge-0/0/0 disable
commit
delete interface ge-0/0/0 disable
commit

However on Juniper box there is way to do it faster outside of JunOS from linux shell
start shell user root
ifconfig ge-0/0/0 down
ifconfig ge-0/0/0 up
This would be equally fast as on Cisco device.
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David SankovskySenior SysAdminCommented:
However on Juniper box there is way to do it faster outside of JunOS from linux shell
start shell user root
ifconfig ge-0/0/0 down
ifconfig ge-0/0/0 up
This would be equally fast as on Cisco device.

That is indeed correct, however in most cases, I don't let users know of this option as root access to a device that acts as a switch is rather dangerous.
Furthermore, since port bounce is most commonly used in tandem with a radius server (meaning all ports have dynamic vLAN assignments) having this option isn't very helpful as a radius server can send radius responses, but not OS level commands to a switch.
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JustInCaseCommented:
Shutting down port and no shutting it again will restart radius access every time it does not matter if interface went down from JunOS or freeBSD.

Additionally, you can disable and enable dot1x on port by issuing commands below and it will restart radius authentication:
set protocols dot1x authenticator interface ge-0/0/0 disable
commit
delete protocols dot1x authenticator interface ge-0/0/0 disable
commit
But, it will take time to perform those commits. :)
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Mohammed ShafayNetwork EngineerAuthor Commented:
Thank you all, for making me understand about port bounce...
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