- By Default, CDP runs on each port of a Catalyst switch, and CDP advertisements occur every
- By Default, MAC addresses are learned dynamically from incoming frames.
- By Default, a Catalyst switch detects an error condition on every switch port for every possible
cause. If an error condition is detected, the switch port is put into the errdisable state and is disabled.
- By Default, ports put into the errdisable state must be re-enabled manually.
- By Default If any errdisable causes are conﬁgured for automatic recovery, the errdisabled port stays down for
- By Default, all switch ports are assigned to VLAN 1, are set to be a VLAN type of Ethernet, and have a maximum
transmission unit (MTU) size of 1500 - Bytes.
- By Default, an 802.1Q trunk uses VLAN 1 as the native VLAN. In the case of an ISL trunk,
using this command has no effect because ISL doesn’t support an untagged VLAN.
- By Default, a switch transports all active VLANs (1 to 4094) over a trunk link
- By Default, a trunk allows all VLANs to be transported across it. If one end of
the trunk is conﬁgured to disallow a VLAN, that VLAN will not be contiguous across the trunk.
- By Default, a switch is in VTP server mode.
- By Default, management domains are set to use nonsecure advertisements without a password. You
can add a password to set the domain to secure mode.
- By Default, every switch operates in VTP server mode for the management domain NULL (a blank string),
with no password or secure mode.
- By Default, a switch uses VTP version 1.
- By Default, VTP pruning is disabled on IOS-based switches. To enable pruning, use the following
global conﬁguration command: Switch(config)# vtp pruning, switch(config-if)# switchport trunk pruning vlan vlan_number (?)
- By Default, PAgP operates in silent submode with the desirable and auto modes, and allows ports
to be added to an EtherChannel even if the other end of the link is silent and never transmits PAgP
packets. This might seem to go against the idea of PAgP, in which two endpoints are supposed to negotiate a channel.
- By Default, BPDUs are sent out all switch ports every 2 seconds so that current topology
information is exchanged and loops are identiﬁed quickly.
- By Default, STP is enabled for all active VLANs and on all ports of a switch. STP should
remain enabled in a network to prevent bridging loops from forming.
- By Default, PortFast is disabled on all switch ports.
- By Default, BPDU guard is disabled on all switch ports.
- By Default, loop guard is disabled on all switch ports.
- By Default, UDLD is disabled on all switch ports.
- By Default, BPDU ﬁltering is disabled on all switch ports.
- By Default, a switch operates in Per-VLAN Spanning Tree Plus (PVST+) mode using traditional 802.1D STP
- By Default, RSTP automatically decides that a port is a point-to-point link if it is operating in full-duplex mode.
- CEF runs By Default
- By Default HSRP PRiority is 100
- By Default HSRP Track will decrement priority - By 10
- By Default HSRP stand- By will prempt active router when its fail
- By Default HSRP hello time is 3 seconds and holdtime is 9 sec
- By Default, all VRRP routers are conﬁgured to pre-empt the current master router if their priorities are greater.
- By Default, every switch port attempts to discover an inline-powered device.
- By Default, QoS is disabled globally on a switch and all QoS information is allowed to pass from one switch port to another.
When you enable QoS, all switch ports are conﬁgured as untrusted By Default
- By Default, a switch instructs an attached IP Phone to consider the PC port as untrusted. The phone will overwrite the CoS values to 0.
- By Default, AAA is disabled, use aaa new-model to enable it.
- By Default Ip Http Server are enabled on cisco switches, you need to disable it for security reasons.
- By Default CAM Table will expired after 300 sec.
feel free to discuss, add more "by default", or to rate this post if it is useful.