Cisco 200-125 Exam

Which statement about slow inter VLAN forwarding is true?

  • A. The VLAN is experiencing slowness in the point-to-point collision less connection.
  • B. The VLANs are experiencing slowness because multiple devices are connected to the same hub.
  • C. The local VLAN is working normally, but traffic to the alternate VLAN is forwarded slower than expected.
  • D. The entire VLAN is experiencing slowness.
  • E. The VLANs are experiencing slowness due to a duplex mismatch.
Answer: Option E.
Explanation: 

Common Causes of Slow IntraVLAN and InterVLAN Connectivity The symptoms of slow connectivity on a VLAN can be caused by multiple factors on different network layers. Commonly the network speed issue may be occurring on a lower level, but symptoms can be observed on a higher level as the problem masks itself under the term “slow VLAN”. To clarify, this document defines the following new terms: “slow collision domain”, “slow broadcast domain” (in other words, slow VLAN), and “slow interVLAN forwarding”. These are defined in the section Three Categories of Causes, below.
In the following scenario (illustrated in the network diagram below), there is a Layer 3 (L3) switch performing interVLAN routing between the server and client
VLANs. In this failure scenario, one server is connected to a switch, and the port duplex mode is configured half- duplex on the server side and full-duplex on the switch side. This misconfiguration results in a packet loss and slowness, with increased packet loss when higher traffic rates occur on the link where the server is connected. For the clients who communicate with this server, the problem looks like slow interVLAN forwarding because they do not have a problem communicating to other devices or clients on the same VLAN. The problem occurs only when communicating to the server on a different VLAN. Thus, the problem occurred on a single collision domain, but is seen as slow interVLAN forwarding.Three Categories of Causes –
The causes of slowness can be divided into three categories, as follows:
Slow Collision Domain Connectivity
Collision domain is defined as connected devices configured in a half-duplex port configuration, connected to each other or a hub. If a device is connected to a switch port and full-duplex mode is configured, such a point-to-point connection is collisionless. Slowness on such a segment still can occur for different reasons.
Slow Broadcast Domain Connectivity (Slow VLAN)
Slow broadcast domain connectivity occurs when the whole VLAN (that is, all devices on the same VLAN) experiences slowness.
Slow InterVLAN Connectivity (Slow Forwarding Between VLANs) Slow interVLAN connectivity (slow forwarding between VLANs) occurs when there is no slowness on the local VLAN, but traffic needs to be forwarded to an alternate VLAN, and it is not forwarded at the expected rate.

Causes for Network Slowness –

Packet Loss –
In most cases, a network is considered slow when higher-layer protocols (applications) require extended time to complete an operation that typically runs faster.
That slowness is caused by the loss of some packets on the network, which causes higher-level protocols like TCP or applications to time out and initiate retransmission.

Hardware Forwarding Issues –
With another type of slowness, caused by network equipment, forwarding (whether Layer 2 [L2] or L3) is performed slowly. This is due to a deviation from normal
(designed) operation and switching to slow path forwarding. An example of this is when Multilayer Switching (MLS) on the switch forwards L3 packets between
VLANs in the hardware, but due to misconfiguration, MLS is not functioning properly and forwarding is done by the router in the software (which drops the interVLAN forwarding rate significantly).

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